Rafael Nadal's knee tendinitis has some tennis commentators calling an end to his grand slam winning career.

Nadal pulled out of last weeks AEGON Championships, won by Andy Murray, with a recurrence of the knee injury that has flared up over the last few years. It's a problem that has many experts fearing that Nadal's career will be finished long before it should be, depriving the sport of one it's most exciting character.

Nadal's knee tendinitis is undeniably a serious problem that could affect the length of his career. However what are the chances of him performing a successful title defence at Wimbledon?

Last year's epic Wimbledon men's final has every chance of being replicated again this year, with the news that Rafael Nadal will be defending his crown. You can watch free live streams of every match at Wimbledon this year with Bet365's live streaming service.

Rafael Nadal successfully came through a three-hour practice session on Tuesday, and will now play in the Wimbledon warm-up exhibition event at the Hurlingham club in a bid to get some much needed grass court practice before he opens centre court proceedings at Wimbledon on Monday.

Nadal missed last year's Davis Cup final because of the recurring  knee problem, and has admitted to being emotionally devastated when a doctor suggested he might never be able to play tennis again.

Nadal's game is incredibly active, based on his physical and mental strength. He has been the iron man of tennis in recent years, able to run faster, further and hit harder for longer periods of time than anyone else on tour.

Because of his knee tendinitis Nadal was advised by doctors that he needed to reduce his overall weight, to reduce the pressure it was putting on his knees, in order to minimise the risk of severe injury.

The decision taken by the Nadal camp to reduce his overall muscle mass for the sake of his knees has two effects. Firstly, Nadal does not have quite the same weight of shot off the ground, and secondly he does not have the same incredible powers of recovery that have stood him in such good stead during each of his Grand Slam wins.

While these effects are only fractional, at the very top level the smallest differences can be the difference between winning and losing, especially when your facing the likes of Roger Federer and Andy Murray.

Furthermore, Nadal's ability to intimidate opponents lessens slightly, meaning they aren't beaten before they even step on court as they may previously have been. His aura of invincibility hasn't been helped by his French Open defeat to Robin Soderling, where Nadal was considered untouchable.

Nadal will be hoping for a kind draw to ease him into Wimbledon, and give him some much needed grass court practice, because he will certainly be vulnerable in the early rounds.

Nadal will be hoping not to face players who can simply hit through him in the same fashion that Soderling did in Paris, and that type of opponent is becoming increasingly commonplace.

As it stands, Rafael Nadal is third favourite for retaining his Wimbledon crown with odds of  4/1 from Victor Chandler, sitting behind Roger Federer at odds of 10/11 from Bet365, and Andy Murray at odds of 3/1 from Paddy Power. 

If Rafael Nadal does retain his Wimbledon trophy, it will be the greatest win of his career, and will force many seasoned tennis experts to eat their words.

Bet on Wimbledon 2009 with Betfair.