The Belgian took the opening set of the match 6-3 and seemed to be on course to reach the quarter-finals but at 1-2 in the second, Clijsters called for the trainer before conceding the match just one game later.

Clijsters will now have to wait a little longer before being able to challenge Caroline Wozniacki for the top spot in the rankings.

Clijsters revealed she has been taking the painkiller Advil since before she won her fourth Grand Slam title at the Australian Open in January.

"With those higher shots against the opponent today, I just feel it pinching a little bit more when I have to do that kick serve and when I have to reach that right arm up higher with the forehand," said two-time Indian Wells winner Clijsters.

Clijsters plans to defend her title in Miami next week. "I'm going to do my rehab there, and plan on playing my first round. I'll just see how it goes every day."

In other fourth-round ties, Ana Ivanovic emerged victorious in the battle of the Serbs, defeating defending champion Jelena Jankovic 6-4, 6-2.

Jankovic, who defeated Caroline Wozniacki in last year's final had opportunities to break the Ivanovic serve seven times but only managed to do so once.

"She played such a great match today," said Jankovic, who had been bidding to become the second woman, after Martina Navratilova in 1991, to win back-to-back titles here.

"She really didn't make a lot of unforced errors. She hit the ball pretty clean, pretty solid. I felt really flat, and she took advantage of all that."

Ivanovic will now go on to play 15th seed Marion Bartoli in the last eight.