Ana Ivanovic's sharp loss of form since she won last year's French Open, and a niggling knee injury, have cast doubts over her title defence at the Paris grand slam which starts on Sunday.
The Serb pulled out of the Madrid Open earlier this month with the recurring injury, which worsened after her country's Fed Cup win over Spain in April.
The 21-year-old from Belgrade vowed to be fit for her French defence but coach Craig Cardon was recently quoted by the tennis channel website (http://www.tennischannel.com) as saying her appearance there was doubtful.
"I am not sure she is even going to be able to play at the French Open because of this knee injury," Cardon said, although he added: "I know her confidence is still pretty high and her level of play is good enough for Ana to win it again."
Even if she plays, the world number eight will need more than confidence to retain her Roland Garros crown after plummeting down the WTA rankings from the number one spot she grabbed after taking last year's title.
She has since won only the Linz Open last October. After another dip in form she was knocked out by unheralded Russian Alisa Kleybanova in the third round of the Australian Open.
If she does miss the French open, Ivanovic will almost certainly drop out of the top 10 - a severe setback after becoming the first Serb to climb to the WTA summit.
Fellow Serb Jelena Jankovic, who ended 2008 as the world number one without ever winning a grand slam title, has had to battle her own problems in a disappointing season.
Her lightning reflexes, stamina and speed around the court, qualities that powered her consistent rise in 2008, disappeared after she gained weight during the Christmas break after building up extra muscle and strength.
Jankovic made a fourth-round exit from the Australian Open and her Madrid quarter-final defeat by Swiss Patty Schnyder has made her drop to fifth in the WTA rankings.
"I expected a lot more of myself in Madrid, but it's history and I now have to raise my game for the French Open," Jankovic was quoted as saying by Serbian media after the loss.
"I know where I have to improve and I also have to make radical changes to be number one again."