Clijsters teamed up with Henin to play for Belgium in the Fed Cup
Belgium's former world number one Kim Clijsters remains a doubt for the French Open after pulling out of next week's Madrid Open with a foot injury.
The 26-year-old US Open champion, currently ranked 11th, has two small tears in the muscles of her left foot.
Clijsters picked up the injury while playing in the Fed Cup tie against Estonia last week.
A full recovery could take up to six weeks, and the French Open gets under way in Paris on 23 May.
Clijsters returned to the WTA Tour last August after a two-and-a-half year break from tennis during which she married and started a family.
Her return reaped immediate rewards as she added a second US Open title to the one she won in 2005.
Earlier this month she thrashed Venus Williams in the Sony Ericsson Open final in Miami.
Clijsters has twice finished runner-up at the French Open, to Jennifer Capriati in 2001 and fellow Belgian Justine Henin in 2003.