The 39-year-old Federer underwent two knee surgeries in 2020 and is targeting a ninth Wimbledon title later this month on his favorite grass court surface.
Federer, who will turn 40 on August 8, defeated Dominik Koepfer 7-6 (7-5) 6-7 (3-7) 7-6 (7-4) 7-5 to set up a meeting on Monday with Matteo Berrettini for a place in the quarterfinals.
“I don’t know if I am going to play,” said the 20-time grand slam winner after his match against Koepfer which ended at 12:45 a.m. local time.
“I have to decide whether or not to continue. Is it too risky to keep putting pressure on the knee? Is it a good time to rest?
“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.
“It may be even more true after a match as long as the one tonight.”
A night curfew due to Covid-19 restrictions ensured the 15,000-capacity Court Philippe Chatrier at Roland Garros was without fans for Federer’s match.
“All the matches I’ve played since the injury are information for the rest of the season,” added Federer.
“It gives me real pleasure to be able to play three hours and 30 minutes at a high level against a very good player. It shows that I’m on the right track.”
Three-time grand slam winner Andy Murray, who has suffered his fair share of injury problems, said it was inspiring to watch Federer play and was testament to the Swiss star’s love of tennis.
“Just seeing Federer at 39 off the back of 2 knee surgeries playing to an empty stadium at 12.30am getting fired up is inspirational to me. Do what you love,” tweeted Murray.
Federer replied: “Thank you Sir Andy, the feeling is mutual. You gotta love it. See you on the grass.”