Nadal suffers comeback blow

(CNN) -- Rafael Nadal's long-awaited comeback has been put on hold after he was forced to withdraw from an exhibition tournament in Abu Dhabi with a stomach infection.

The 26-year-old, who has not played since his shock second round defeat by world number 100 Lukas Rosol at Wimbledon, had hoped to make a return to action following a six-month absence with a knee injury.

Nadal is desperate to be fit for the ATP tournament in Doha on December 31, but now faces an uphill struggle to make the event.

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The 11-time Grand Slam winner was set to play at a six player exhibition competition this week alongside the likes of world number one Novak Djokovic and U.S. Open champion Andy Murray.

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But the Spaniard has taken to Facebook and Twitter to reveal he will now be unable to compete after pulling out of the tournament following advice from his doctor.

"I am really sorry but I cannot compete this year in Abu Dhabi," wrote the seven-time French Open champion and presently ranked number four in the world.

Nadal to make long-awaited tennis return

"Everything was ready and I was really eager to return to competition, but the doctors have forbidden me to participate in Abu Dhabi because of a viral infection of the stomach which has provoked a fever."

The news comes as blow for Nadal, who is desperate to get back on the court and make up the ground on his rivals.

After his shock defeat at Wimbledon, Nadal was diagnosed with Hoffa's syndrome, an inflammation of the fatty tissue in his left knee which has plagued him in recent years.

The injury prevented him from defending his Olympic title at London 2012, while he also missed out on the U.S. Open and Spain's Davis Cup final defeat by the Czech Republic in November.

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But speaking earlier in the week, he insisted that his knee was now in better shape with the new season upon the horizon.

"I haven't forgotten how to play. I have played over 600 ATP matches and I have spent two years without playing.

"My feeling is good. I won Roland Garros and those emotions are still me," he said.

"The doctors say the knee is fine and that is great news for me. I still feel something, it's not perfect."