Fifth seed Marat Safin has been forced to pull out of this week's US Open in New York because of a knee injury.
The 25-year-old Russian, who won the Flushing Meadows tournament in 2000, has been bothered by tendinitis in his left knee for most of the summer.
He took six weeks off before returning to action earlier this month at Cincinnati, where he lost to Robby Ginepri in the quarter-finals.
Safin was scheduled to face Alexander Popp of Germany in the first round.
But Popp will now face fellow German Bjorn Phau, a 'lucky loser' from the qualifying competition.
A statement on Safin's personal website said: "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.
"He will return to Italy to continue treatment and ensure that his knee is fully recovered.
"It is not known how long he will be out but this time he will make sure he does not rush into returning.
"Marat still wants to play tennis and he will be back."
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 and then missed seven weeks of competition when he underwent surgery to repair a knee ligament tear. Safin missed Russia's 3-2 Davis Cup quarter-final win over France in July.