Fifth seed Marat Safin [Images] has withdrawn from the U.S. Open which starts later on Monday because the knee injury which sidelined the Russian for seven weeks earlier this year is still troubling him.

Safin, 25, admitted two weeks ago that he had returned to the tour against doctors' advice to try to prepare for the U.S. Open, one of his favourite events.

He won his first Grand Slam title at Flushing Meadows in 2000.

"Although Marat wanted more than anything to play and has tried whatever he could to be ready, as a professional tennis player he has had to admit his body is saying it is too soon," said a statement on Safin's personal website.

"He has made the decision after discussions with all those around him. He is not depressed because he realises this is the right thing to do."

The statement said the Australian Open [Images] champion would return for treatment in Italy [Images] where he previously had keyhole surgery on the knee. It was not clear how long he would be out of action.

"This time he will make sure he does not rush into returning. Marat still wants to play his tennis and he will be back," added the statement.

After winning the Australian Open in January, Safin struggled to regain form and concentration as his knee began to affect him.

He lost in the third round of Wimbledon [Images] and then missed seven weeks of competition when he underwent surgery to repair a knee ligament tear.

Safin missed Russia's [Images] 3-2 Davis Cup quarter-final win over France [Images] in July.

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