updated 4:30 p.m. ET May 5, 2005

BERLIN - Kim Clijsters slid awkwardly as she chased down a ball in her third-round match at the German Open. She tried to keep playing, but the pain in her knee was too much to bear.

Clijsters retired in the second set, and now her status for the upcoming French Open is in doubt.

While Clijsters waits for the swelling in her right knee to subside, Maria Sharapova and Justine Henin-Hardenne are set to meet in a blockbuster quarterfinal matchup. Sharapova, who can become world No. 1 with a title here, beat Shuai Peng of China 6-2, 6-1 while Henin-Hardenne won her 13th straight match, 4-6, 6-4, 6-2 over Kveta Peschke of the Czech Republic.

“Clay is my best surface, but it won’t be that easy,” Henin-Hardenne said. “We know how good and strong Sharapova is. She’s very confident right now.”

So was Clijsters, who entered Thursday with victories in 19 of her last 20 matches. After she injured her knee against Patty Schnyder, Clijsters received court-side treatment but gave up a short time later. Clijsters had won the first set 7-6 (4) and was trailing 6-5 in the second.

The French Open starts May 23.

“I just have to wait two days for the MRI. Maybe I’ll be back to play the French Open,” Clijsters said. “I can only hope for the best. It’s very frustrating.”

She is even considering skipping the punishing clay-court season to spare her increasingly fragile body.

“Maybe it’s a lesson — I’ll just forget about the clay-court season,” said Clijsters, who returned in mid-February from a 10-month layoff with a left wrist injury.

Henin-Hardenne is on a streak of her own after overcoming a virus and injuries. In March at Miami, she and Sharapova met for the first time, and Henin-Hardenne was pleased to stretch the Russian teenager to three sets in her comeback tournament.

Henin-Hardenne hasn’t lost since then, but she has been tested here. She was pushed to three sets for the third straight match.

“It’s not a problem unless you go home early,” Henin-Hardenne said. “I need the practice and I get stronger in the second and third sets.”

Sharapova has coasted through this tournament with two straight-set wins. The only thing that has bothered her: overcast skies.

“I don’t like this cold weather — I’d rather have it sunny and warm,” said Sharapova, born in Russia but raised in Florida. “I feel relaxed and good, but I haven’t had a real test yet.”

In the other matches, second-seeded Amelie Mauresmo beat Virginie Razzano 6-4, 6-2, fourth-seeded Svetlana Kuznetsova rallied past Conchita Martinez, sixth-seeded Nadia Petrova of Russia defeated Mary Pierce 6-2, 7-5, eighth-seeded Elena Bovina downed American Meghann Shaughnessy 6-4, 6-2 and 13th-seeded Jelena Jankovic of Serbia-Montenegro ousted German wild card Julia Schruff 6-3, 6-2.

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