Roger Federer is considering withdrawing from the French Open despite reaching the last 16 after a tense four-set victory over Dominik Koepfer in a tie which finished just before 12:45 on Sunday morning.
"I don't know if I am going to play," said Federer, who is just two months shy of his 40th birthday and is due to play Italy's Matteo Berrettini in Monday's fourth round.
"I have to decide whether or not to continue playing. Is it too risky to keep putting pressure on the knee? Is it a good time to rest?"
The 20-time Grand Slam title winner, who underwent two knee surgeries in 2020, and is playing only his third tournament since last year's Australian Open, has always said Wimbledon is his priority this year.
He is chasing a ninth title at Wimbledon which starts on June 28.
He is also scheduled to play the warm-up grass court tournament in Halle beginning on June 14, the day after the French Open ends.
"Every match I have to reassess the situation and see the next morning in what state I wake up and how my knee is doing," added Federer after being on court for 3 hours and 35 minutes.
"It may be even more true after a match as long as the one tonight."
Saturday's match, which spilled over into Sunday, was played in an eerily-empty Court Philippe Chatrier devoid of fans due to a government-imposed Covid-19 curfew.