Novak Djokovic has been forced to withdraw from his French Open quarterfinal against Casper Ruud due to the right knee injury he sustained in his fourth-round win Monday.

The move ends his title defense and means he will relinquish the No. 1 ranking.

Djokovic underwent an MRI scan and further medical tests on his knee Tuesday. A statement from Roland Garros said he suffered a “torn medial meniscus” of his right knee.

Djokovic said Monday he was hurt in the second set of his eventual five-set win over Francisco Cerundolo. He was hopeful of competing in his quarterfinal Tuesday.

The 24-time Grand Slam champion said he had slight discomfort in his right knee coming into the tournament but had no further issues until his mammoth fourth-round match Monday. His third-round match finished at 3:07 a.m. on Sunday and he said that late finish “didn’t help the sleeping, the biorhythm, and recovery.”

After taking the first set against Cerundolo, Djokovic said a slip in the third game of the second set “affected the knee.” He requested a medical timeout and had further physio treatment on it during the match.

Djokovic was visibly frustrated with how slippery he was finding the surface on Court Philippe-Chatrier and asked for it to be swept more frequently. But the request was rejected.