PARIS -- French number one Sebastien Grosjean is doubtful for his country's Davis Cup semifinal against the United States at Roland Garros next weekend, France's captain Guy Forget has said.

Grosjean suffered a back injury in training last week and may not have recovered in time to play Friday's singles.

"For the time being, I need to talk again with the players, the staff and the doctor... even if I have an idea of my own," Forget told reporters on Wednesday.

Grosjean was unable to train last weekend because of the back problems.

Should he be forced out of the match, he would be replaced by up-and-coming Paul-Henri Mathieu, the last player to have beaten U.S. Open champion Pete Sampras.

"Sebastien can be surprising in his ability to recover from injury, like he showed by reaching the semifinals in Monte Carlo just after being injured in Pau," Forget said.

Grosjean had his whole clay-court campaign in Spring hampered by a groin injury sustained in a previous Davis Cup match against the Czech Republic in April.

"As for Paulo (Mathieu), he's ready. He's young... he's injury free.

"I feel he's ready and he can step in. If I call him, it's because I know he can beat Andy Roddick and James Blake," Forget said.

Mathieu, who beat Sampras in Long Island, shortly before the U.S. Open, had taken Andre Agassi to five sets in the French open on the same Roland Garros center court on which the semifinal will be played.

Sampras and Agassi elected not to play against France and without Grosjean, the match would turn into a more low-key affair.

Arnaud Clement is expected to be France's other singles player in the match. The draw will be announced on Thursday.