Novak Djokovic sparked concerns about his injured knee for the rest of his French Open title defense, with the top seed saying he briefly considered pulling out midway through his five-sets win over Argentine Francisco Cerundolo on Monday.

The 37-year-old had to dig deep for a second straight match after a third-round marathon against Lorenzo Musetti and needed medication during a 6-1 5-7 3-6 7-5 6-3 win over Cerundolo that sent him to the quarterfinals after four hours and 39 minutes.

Djokovic said he had been experiencing slight discomfort in his right knee for a couple of weeks and the issue flared up as soon as he slipped and tweaked it during the third game of the second set.