Injury heartache for Williams

(CNN) -- Venus Williams' hopes of landing a fourth Miami Masters title were left in tatters after the U.S. star was forced to pull out with a back injury.

The seven-time grand slam champion withdrew ahead of her third round clash with fellow American Sloane Stephens Saturday.

Williams, ranked 18th in the world, had hoped to shake off the problem following her win over Japan's Kimiko Date-Krum.

It is the latest setback for the 32-year-old, who in 2011 fought back from Sjogren's syndrome, an auto-immune disease which causes fatigue.

Read: Venus vows to rise again after illness

"Yesterday I was having some pain, and then just wanted to see how I felt in the warmup -- just not able to play today," Williams told reporters.

"It's really disappointing. This is just the kind of tournament you want to play well at.

"But I have faced disappointments in my life and my career. It's not the first, probably not the last, just have to get through it and stay positive."

Williams now hopes to return to action in Charleston, South Carolina next month.

"I've dealt with injuries before in my whole career," she said. "I know how to hopefully recover quickly from them.

"I'm playing in Charleston, so that's really still my goal, to get ready to play there."

Read: How do you solve a problem like Maria? Don't ask Wozniacki

Her younger sister Serena went through to round four -- despite needing to resort to riding a bike to the event due to traffic problems.

The top seed and five-time Miami champion battled to a 6-3 6-3 win over Japan's Ayumi Morita to set up a meeting with Slovakian 13th seed Dominika Cibulkova.

Venus Williams wasn't the only big name to leave the tournament Saturday as Caroline Wozniacki crashed out after suffering a shock defeat by Spanish wild card Garbine Muguruza.

The World No. 9 was stunned 6-2 6-4 just a week after losing out in the final at Indian Wells to Maria Sharapova.

Muguruza, ranked 73rd in the world, will now take on Li Na in the fourth round.

Chinese star Li saw off American Varvara Lepchenko 6-2, 6-4 as she continued her comeback from injury.

Read: Tennis to land in Li Na's hometown

The World No. 5 had been out of action for seven weeks after suffering an ankle injury during her Australian Open defeat by Victoria Azarenka.

But while Li is still in with a chance of glory, Azarenka's hopes are over after she was forced to withdraw with an ankle injury of her own.

"It was really obvious what the decision was couple days ago already," Azarenka told reporters. "I just wanted to give my 100 % possibility to play and today was my last test."

Read: Redfoo's party rock can't lift tennis ace Azarenka's injury gloom

Maria Sharapova will be hoping to progress to the fourth round Sunday when she takes on fellow Russian Russian Elena Vesnina.

Sharapova, who won at Indian Wells last weekend, eased past Canada's Eugenie Bouchard 6-2 6-0 Friday following a power outage.

In the men's section, last year's runner-up Andy Murray eased into the third round with a comfortable 6-3 6-1 victory over Australia's Bernard Tomic.

Murray, who won the tournament back in 2009, will face Grigor Dimitrov next after the Bulgarian overcame Simone Bolelli.

"No matter how you start your match you need to make your opponent work hard," Murray told Sky Sports after seeing off a disappointing Tomic.

"I didn't hit it unbelievable today but I worked hard. Once I got the breakthrough he made mistakes. But it is unbelievably hot and windy.

"It's tough to feel comfortable, maybe more than my opponent because I am used to the court and the wind and the humidity."

Read: Andy Murray's five-star hotel venture

Elsewhere, Sam Querrey survived an almighty scare to win his first match since becoming the U.S. No.1.

Querrey overcame Lukasz Kubot 4-6 6-3 6-3 to secure his place in the next round.

"I started out a little slow," he told the tournament's official website.

"He broke me the first game, but then he served really well rest of the first set.

"But after that, I felt pretty good second and third sets. I served big and hit my forehand well. I was pretty happy."

There were also wins for France's Jo-Wilfried Tsonga, Italy's Andreas Seppi, Belgium's David Goffin and eighth seed Richard Gasquet.

Read: Tennis serves up new measures in the fight against doping

Sunday's action is set to include World No.1 Novak Djokovic, who is looking to win a fourth Miami Masters title

Djokovic, who destroyed Lukas Rosol 6-1 6-0 Friday, will take on India's Somdev Devvarman, currently ranked 254th in the world.

But one man who won't be on court is fifth seed Juan Martin del Potro after he was sent crashing out in the second round by Tobias Kamke.

Del Potro reached the final at Indian Wells last week, but was unable to see off 89th ranked Kamke.

"I was excited to play here, but [it was] just a bad day and he [played] really well," the Argentine told the tournament's official website.

Via: Injury heartache for Williams

Djokovic, Sharapova battle into last 16

(CNN) -- Novak Djokovic and Maria Sharapova progressed to the fourth round of the Miami Masters on Sunday, neither impressed with their form as they battled windy, hot conditions.

Djokovic, seeking to emulate Andre Agassi -- the only man to win at Key Biscayne three years in a row, from 2001-03 -- beat 254th-ranked Indian Somdev Devvarman 6-2 6-4.

"It was very difficult to kind of get into a rhythm because you couldn't really serve at 100% and you had to go more for precision and put twice as much effort into the step adjustments because of the windy conditions," said the world No. 1, who will next face veteran German Tommy Haas in the 10-day hard-court event.

"All in all, I'm just happy to get through the rough day."

Djokovic, seeking his fourth Miami crown, having also won in 2007 as well as losing the 2009 final, was joined in the last 16 by Spanish third seed David Ferrer, who will next play Japan's No. 13 Kei Nishikori.

Read: Sisterly love drives Radwanskas

The Australian Open champion's fellow Serbian Janko Tipsarevic, the seventh seed, will next face French No. 11 Gilles Simon.

Sharapova has been in four title matches in Miami, including the last two, and come away emptyhanded every time.

She is seeking to become only the third woman to win the Indian Wells/Miami double in the same season, and kept alive her hopes with a 6-4 6-2 win over fellow Russian Elena Vesnina, the 29th seed.

"It wasn't easy for the both of us with the heat and the wind," said the world No. 2, who is seeded third.

"It was just one of those days where you know you might not be playing your best tennis -- I certainly wasn't today.

"But I got through, and I'm onto the next one."

Read: Redfoo's song for Azarenka

Sharapova will next face 21st-seeded Czech Klara Zakopalova, who upset another Russian when she beat No. 14 Maria Kirilenko 6-2 7-6 (7-4).

Sharapova lost to the 31-year-old when she was just 15, back in 2003 at the Australian Open, but has won their last four meetings including a last-16 match in Qatar this year.

Romania's Sorana Cirstea earned a clash with former world No. 1 Jelena Jankovic after eliminating German sixth seed Angelique Kerber 6-4 6-0.

"I didn't have any expectations coming into this tournament because I've never played that well in Miami," the Romanian 28th seed said.

Read: Injury blow for Williams

"But I've been fighting the best I could and working my way through every single match, and it's working."

Jankovic, the 2008 runner-up, beat Russian 11th seed Nadia Petrova 7-6 (9-7) 6-4.

Alize Cornet ended the hopes of 19-year-old American Lauren Davis, who was allowed into the main draw when second seed Victoria Azarenka pulled out due to ongoing ankle problems.

The French 32nd seed came from behind to win 2-6 6-3 6-2 and earn a clash with either Italian Roberta Vinci or Spain's Carla Suarez Navarro.

Via: Djokovic, Sharapova battle into last 16

Redfoo's party rock can't lift Azarenka's gloom

(CNN) -- Her popstar boyfriend has written a song about her "heart of a champion," but Victoria Azarenka is struggling to get on court at the moment.

The Belorussian is unbeaten in 17 matches this year, but she has now suffered her third withdrawal of the season after a late pullout at the Miami Masters on Friday.

She cited the ankle injury that forced her to miss last week's quarterfinal against Caroline Wozniacki at Indian Wells, allowing Maria Sharapova to take the No. 2 ranking spot from her.

"The last two days I tried to practice, which did not get better so it just gives me a very obvious indication that it's not possible for me to play," Azarenka told reporters at Key Biscayne, where she was champion in 2009 and 2011 and this year had a first-round bye.

"Today I went on the court and I got more pain. I cannot really move. It makes me very frustrated."

The Australian Open champion has been dating LMFAO's Redfoo, whose new song "Heart of a Champion" samples the tennis star's trademark grunting and includes the lines "You gotta start aggressive, Keep your feet moving, You gotta really want it, With everything you're doing."

It even apparently alludes to her controversial Australian Open semifinal against Sloane Stephens, when the 23-year-old angered fans by taking a lengthy medical break at a crucial point in the match against the U.S. newcomer, citing breathing difficulties.

The chorus includes: "When you're losing your breathing, Your body is sore, To be the last one standing, In the eye of a storm, It takes the heart of a champion."

Redfoo, the son of Motown Records founder Berry Gordy, is a keen tennis player himself and has entered in regional qualifying playoffs for this year's U.S. Open.

The 37-year-old rapper will try to get through in both singles and doubles, in which he will partner Ayaka Okuno, 17, who he has been coaching.

"It's always been a dream of mine to play professional tennis," he said in a statement last week.

Azarenka's withdrawal allowed 19-year-old Lauren Davis into the main draw, and she took her chance -- saving three match points against Madison Keys before beating her fellow American 6-1 5-7 7-6 (9-7) in the second-round match.

There was also a walkover in the men's event in Miami, as third seed David Ferrer progressed to the third round after Russia's Dmitry Turnsunov pulled out due to illness.

The Spaniard will next play Italian 32nd seed Fabio Fognini.

Via: Redfoo's party rock can't lift Azarenka's gloom

Bromance of 'marathon men'

Open Court is CNN's monthly tennis show. Click here for program times and latest features.

(CNN) -- You'd think John Isner and Nicolas Mahut would be sick of the sight of each other.

But from the ashes of their record-breaking marathon match at Wimbledon in 2010 -- officially the longest in tennis history -- an enduring "bromance" has blossomed.

It had to, after the pair walked on court for a low-key first-round match in the men's singles draw, limping off three days later after 11 hours of tennis, battered, bruised, fatigued, but lauded as heroes the world over.

Even if either should go on to win a glut of major titles in their respective careers, it is entirely possible they will still forever be known for "the marathon match."

Read: U.S. grand slam drought: Is the NFL killing American tennis?

Far from resenting the attention their epic encounter brought them, the pair are firm friends; not surprising, given they are the only players on the planet to know just how much that eight-hour final set, which ended 70-68 in Isner's favour, can take from you.

"I'm actually really close with him," Isner told CNN's Open Court.

"Prior to that match, I knew him but it seemed in passing, I'd give him a head nod, nothing more than that but from that match, I've realized that he is one of the nicest, classiest guys on tour.

"He actually is a really good friend of mine. We keep in touch all the time so we developed a friendship from that match, obviously sharing a court for three days."

Isner is now officially the highest ranked American in the world following Andy Roddick's retirement, but try as he might to move on from the marathon match it is almost always top of the list when tennis fans approach him.

So what was it like to be involved in an episode that transfixed the world?

"Yeah, it was crazy. I don't think people will remember the fact that I won that match. I think it would be more the fact that we played it ... Nicolas Mahut, he was a warrior that day," Isner said.

"I do hear it all the time, it's something that's going to stick with me forever but I've feel like I've done some things out of that match. I've broken the top 10.

"I had a few marquee wins under my belt so I've done some good things to try to shed that label but it's up to me to keep doing more."

Many expected a tight encounter, given the serving prowess of both players and Isner won that battle too, firing down 112 aces compared to Mahut's 103.

For a player who stands at 6 foot 9 inches, Isner's serve is undoubtedly the most powerful weapon in his armory. When it fires, few in the world can live with him, even in this golden age of Federer, Murray, Djokovic and Nadal.

He has five ATP Tour titles to his name, winning twice at the Newport and Winston-Salem events. Last weekend he competed at Indian Wells, where in 2012 he saw off world No. 1 Novak Djokovic before losing to Roger Federer in the final. On Saturday he was beaten in his opening match by Australian veteran Lleyton Hewitt.

"If I can get that opportunity where I can play those guys ranked in the top five of the world, that's when I usually see myself raise my game," Isner explains.

"I like playing on those big stages and I think that's one of the main reasons why I beat Federer, I beat Djokovic and I almost beat Rafa at the French Open of all places. That's why you play this game -- to get a crack at those guys, try to take it to them.

"Outside of my serve, I think my forehand is my best shot," he added. "It's no secret. My game isn't rocket science. The more aggressive I am, the better my results are going to be.

"I have to be really aggressive with my forehand. Something that I'm constantly working on. I need to return better. If I can do that, I'll see a lot more success but my serve is my weapon and that's something that I rely on all the time."

But while that towering frame benefits his imposing serve, it can also hinder his movement around the court. No surprise then, that Isner invests a huge amount of training time on improving his on-court coverage.

"I'm always trying to work on my weaknesses which in the main part is my movement. I can improve that aspect.," he said.

"If I can improve my movement just a little bit, my game will improve a lot so other than that, my height certainly helps me with my serve first and foremost but it's also a bit of a detriment when it comes to moving around the court."

"The game is pretty physical today where you see these guys running down balls. You can't hit a winner on some of these guys but for me, that's not the case."

Isner may have found it difficult to shake off the "marathon man" tag but there are some other things that have stuck with him by his own choosing -- like his love for wrestling.

The spectacle of World Wrestling Entertainment may not be to everyone's tastes but Isner and his friends still gather round to watch it every week.

"Although it is scripted, I do have great respect for these guys. A lot of guys make fun of me but these guys are actually putting their bodies on the line," he said.

"Growing up in North California, me and all my friends, it was pretty sad but our weeks revolved around a Monday night.

"Monday night wrestle would come on and we'd all huddle up and pay per views would come on and I'd get 10 of my friends to come over -- $5 each, so we could pay the $50 to watch the pay per view.

"It's something that I've always liked and I haven't grown out of it either. You know, at 27 at 6 ft 10 ins, I haven't grown out of that stage so for me, it's something I do to pass time on Monday nights."

Via: Bromance of 'marathon men'

Serena victorious on return in Miami

(CNN) -- Serena Williams shook off any rustiness after a month-long break from competitive tennis as she launched her quest for a sixth Miami title with a straight sets victory over Italian Flavia Pennetta.

The world No. 1 hasn't played since losing to Victoria Azarenka in the final of the Qatar Open on February 17 but made light work of her unseeded opponent winning 6-1 6-1.

Williams, a 15-time grand slam winner, pulled out of the Dubai Tennis Championships after her defeat in Doha complaining of a back injury but looked in good touch as she raced to victory in just under 80 minutes.

"I think I missed a few shots, but only because I think I was off footwork-wise," she told reporters. "But it's always just good just to win a match and stay in the tournament and keep going.

Read: Radwanska girls' grand slam ambition

"I felt like I should be putting the balls away for my opponent but she was so quick and she was running every ball down."

As for coming into the tournament as the world's best player she said: "It always feels better when you're No. 1. There's nothing like when they announce you and they say, the No. 1 player in the world.

"It definitely gives you a little bit more confidence ... a little more pep in your step. I have a lot of matches to play. If I can just stay relaxed -- I really feel like I can do it, but, you know, I'm sometimes my own worst enemy."

Defending champion and No. 4 seed Agnieszka Radwanska, from Poland, breezed into round three with a 6-3 6-2 victory over Taiwan's Hsieh Su-Wei.

"I was happy to have a quick match," Radwanska was quoted as saying on the WTA Tour's official website. "The first match is always a little bit tough and tricky, especially after Indian Wells, where we had a little bit of different conditions.

"It was a really special tournament for me because I was really playing a lot of good matches against top players and not even losing a set.

"I definitely have great memories from here. And the final was a very good match. Hopefully I can play the same level of tennis this year. I will do everything to hold the trophy again."

China's Li Na, seeded fifth, was also making a return after spending six weeks on the sidelines with an ankle injury but she eased past Dutchwoman Kiki Bertens 6-3 6-1.

"I wasn't nervous before the match today, I was excited," Li told the WTA Tour website. "For the last six or seven weeks I haven't played any tournaments so I was happy to win my first match after such a long time.

"There were a lot of fans there to support me today, I was like, 'Wow!' My game was pretty good today, I followed the plan of what I should do. I just had to believe in myself that I could do it."

Petra Kvitova, the 2011 Wimbledon champion defeated China's Peng Shuai 5-7 6-2 6-2.

Via: Serena victorious on return in Miami

Sisterly love drives grand slam ambition

(CNN) -- It has only ever happened between two sets of sisters in the history of tennis, but Agnieszka and Urszula Radwanska could yet become the next female siblings to meet in a major final.

Way back in 1890, in only the fourth edition of what would become today's U.S. Open, Ellen Roosevelt -- a first cousin of future President Franklin D. Roosevelt -- beat her sister Grace, a feat that would be unmatched for more than a century.

When it did happen again, at the U.S. Open in 2001, it marked the first of eight grand slam finals between the Williams sisters -- with Venus beating younger sister Serena on the first occasion, but losing six of seven since.

With Urszula having risen from 109th to 31st in the rankings during the 2012 season, her trajectory suggests there is every chance that the Radwanska sisters -- both of whom won Wimbledon as juniors -- could one day meet in a grand slam final.

Read: Serena Williams on what it's like to play Venus

They have met in a grand slam before, with Urszula -- the younger at 22 -- briefly losing her usual cool en route to defeat in the first round of the 2011 U.S. Open.

"I don't ever want to play her in the first round, but in the final -- no problem," laughs 24-year-old "Aga," whose total prize money of $12 million dwarfs that of her sibling's $1 million, reflecting her higher status as world No. 4.

Almost identical

While the Poles' less powerful version of tennis will never be a match for the record-breaking Williams duo, one thing they do share with the Americans is a tight bond.

"We are best friends, we are so close," Urszula told CNN's Open Court. "We have always been together -- participating, living and traveling together -- so it is nice to have my sister on tour.

"We share things, we go shopping and we have a good time, so sometimes when I am traveling alone without her I feel so lonely."

The feeling is so mutual that precisely the same words come out of her elder sister's mouth.

"My sister and I have been traveling everywhere together for the last 18 years -- the same school, same practice," Agnieszka says. "We are best friends, we are so close."

Save for their hair color -- with Aga a brunette and Urszula a blonde -- and the 21 months that separate their dates of birth, there is little between them, says the firstborn.

"We are very similar personalities -- we like to have fun," says one of the female circuit's most popular players. "When we are on court, we like to work hard. But off the court, we try to have fun and relax, go to the cinema and forget about tennis.

"What's different about us? We like some different food! There's not much difference."

Pride of Poland

Unlike the Williams sisters, whose homeland had been previously represented by such greats as Martina Navratilova, Chris Evert and Billie-Jean King (and that's not even mentioning the men), the Radwanskas are putting their country on the tennis map.

Prior to them, just two Poles had made noteworthy contributions to international tennis.

In the late 1970s, Wojtek Fibak reached the Top 10 on the men's ATP Tour while much further back, Jadwiga Jedrejowsa reached three grand slam finals in the 1930s which -- even if she didn't win one -- is still the Polish record for the Radwanskas to beat.

Aga made her own slice of history in 2007, becoming the first Pole to win a WTA singles title when as an 18-year-old she beat Russia's Vera Dushevina in Stockholm's Nordic Light Open.

She has pressed on since, adding a further 11 WTA titles and reaching her highest ranking of No. 2 in 2012, a year when she reached her first grand slam final -- albeit beaten by (who else?) Serena Williams at Wimbledon.

Nonetheless, she was the first Pole to contest a grand slam final since the Open Era began in 1968 -- even if her defeat meant she missed out on a long-held dream.

"I was really close to being world No. 1 a few times in 2012 but unfortunately I didn't make it," she says. "Hopefully, I will have another chance in 2013. That is the goal I have been working for for so many years -- to be number one, even for one week."

After a slower start, Urszula -- currently ranked 37th -- may feel as though she is beginning to make her mark, with 2012 having proved a breakthrough year following a back problem that hindered her early progress as a professional.

She may never have progressed past the second round of any grand slam singles event, but she did break into the top 30 for the first time and reached her first WTA Tour final at the UNICEF Open in the Netherlands.

"I am very happy for her that she is doing well," says Agnieszka. "She is working really hard for that, she has been through a lot of things and I am happy that she has made the top 30 already.

"Hopefully, I'll see her in the top 10 very soon -- there's a big chance."

Fatherly guidance

Much like Serena and Venus, the Poles were first taught by their father -- although in contrast to Richard Williams, Robert Radwanska did have a coaching background prior to his daughters' births.

Those searching for differences can point to Agnieszka's birthplace of Krakow differing to Urszula's in Gronau, since her father was then working in the north-western German town as the local tennis pro.

His profession meant the girls were surrounded by tennis from birth, with early images showing the sisters in the midst of bats and balls -- and one memorable picture showing them tottering around like ballerinas, albeit with their feet squeezed into tennis ball canisters.

Their father coached Aga and Urszula from the ages of five and four respectively but he stopped traveling last year, and both are now working with Borna Bikic (Jelena Dokic's former coach) as well as Polish Fed Cup coach Tomasz Wiktorowski.

Nonetheless, Robert still trains his girls whenever they go home to Krakow.

"This is our home so we love coming back," says Urszula of Poland's second largest city. "Our family is here but it's good that I have a sister so I can always practice with her. I don't have to find a hitting partner and also our coach is our dad, so it's perfect."

The historic city is by no means perfect for the tennis professionals -- it has no hard court, for example -- but its enduring appeal for the girls more than makes up for that.

"It's always a great feeling to be here, especially since we are traveling 10 months a year," says Aga. "Even if I can only go home for two days, I will as it's always nice to just sit on my couch, watch TV and be in my kitchen. Those two days make a huge difference -- it feels like I have a normal life."

For the rest of the year, the sisters are largely on the road -- sometimes together, sometimes not -- and they always find a way of staying in contact.

"When something's happened to me, Aga is the first to know," says Urszula. "We talk to each other all the time -- on Skype, over the phone, texting. We are always in touch."

Sister act

More often than not, they are normally in the same place -- and not just playing singles, but also teaming up for doubles together.

In London last year, where Agnieska was honored to be Poland's Olympic flag bearer, they had mixed fortunes, exiting the Games in the second round before withdrawing from the third round at Wimbledon to help Aga, suffering from illness, in her singles bid.

With a WTA doubles title already to their name, at Istanbul in 2007, the next step is to join the select band of sisters to have won a grand slam doubles title -- with the Williams and Roosevelts joined only by Ukrainians Alona and Kateryna Bondarenko in the history books.

Even if they fail, one thing is for sure -- the Radwanska sisters are inspiring the next generation of Polish tennis players.

"I can clearly see that tennis in Poland is getting better. A lot of kids are trying to play right now and trying to be professionals -- so it's nice to see that -- and people are talking more about tennis so it's becoming more popular," says Urszula.

"And when I see Aga having great results, I want to be the same or even better."

Via: Sisterly love drives grand slam ambition

Nadal urges tighter drugs control

(CNN) -- Rafael Nadal has called for stricter doping controls and more transparency to help eradicate drug cheating in tennis.

Nadal wants to ensure tennis is not plagued by the doping problems which have affected so many other sports, notably cycling, following the Lance Armstrong saga.

Read: Federer: 'Naive to think tennis is clean'

"It's something even I don't like to talk about because it has damaged the image of sport, and sport doesn't deserve this kind of thing in my opinion," the 11-time grand slam champion told CNN's Open Court show before his weekend triumph at Indian Wells.

"When somebody like Armstrong was an idol for most of the people who loved sport, at the end, you see that was not true.

"It's a big disappointment, so I think we need to work together in the same direction to change the situation. It cannot continue like this.

"We need to be stricter on a few things. We need to have all the controls made public."

Read: Nadal battles back for Indian Wells triumph

Nadal, who made his return to action in February following a seven-month absence with a knee injury, said tennis needs an all-encompassing approach to drug testing in order to maintain the sport's image.

"We have to work together, we have to be working together with the administrators and hopefully we can change that terrible situation," he said.

"We are lucky that in tennis, it has happened in just very exceptional cases but at the end, tennis is in sport, so if that happens in other sports, it affects tennis too."

In recent months sport has been hit by several high-profile doping scandals.

Cyclist Armstrong was stripped of his seven Tour de France titles, while Australian sport was given a wake-up call after a government report alleged athletes were using illegal substances supplied by organized criminal groups.

Cheating in sport: What are banned substances?

Football's governing body FIFA has already stated its intention to introduce biological passports, while the outcome of the Operation Puerto trial in Spain into the relationship between sport and doctor Eufemiano Fuentes' doping network is ongoing.

Biological passport

The International Tennis Federation (ITF) recently confirmed that it will introduce a biological passport program, a system similar to the one used in cycling, where players' drug test results are kept over a long period of time so that the use of illegal substances is more easily detected.

"The implementation of the athlete biological passport is an important step in the evolution of the tennis anti-doping program as it provides us with a great tool in the fight against doping in our sport," said ITF President Francesco Ricci Bitti.

In 2011 the ITF and the World Anti-Doping Agency conducted just 21 out-of-competition blood tests in a bid to detect illegal products such as human growth hormone (HGH), EPO, transfusions and other blood-doping substances.

According to the latest figures, the vast majority of tests in tennis in 2011 -- 2,019 of a total of 2,150 -- were urine.

Read: Fish furious as Odesnik prepares to return from drug ban

In February, the ITF banned Czech Republic player Barbora Zahlavova Strycova for six months after she tested positive for the stimulant sibutramine at a tournament in October.

She insisted the drug had made it into her system through a supplement and denied taking it to enhance her performance.

In 2010, former top 100 player Wayne Odesnik, was suspended by the ITF after Australian customs officials found eight vials containing HGH in his luggage.

He denied using HGH and never tested positive for it.

His two-year ban was cut in half because the ITF said Odesnik cooperated with its anti-doping program.

Earlier this month, 17-time grand slam champion Roger Federer told CNN that it was "nave" to think tennis is clean, while world No. 1 Novak Djokovic recently queried the declining number of blood tests he had undergone.

"I wasn't tested with blood for the last six or seven months," he told reporters. "It was more regularly in the last two, three years ago. I don't know the reason why they stopped it."

Via: Nadal urges tighter drugs control