Roger Federer says he may withdraw from the French Open as he assesses the physical impact of his epic third round win over Dominik Koepfer on Saturday.

The 39-year-old Swiss prevailed 7-6 (7-5) 6-7 (3-7) 7-6 (7-4) 7-5 over Koepfer in the longest match he has played in 18 months, following double knee surgery, lasting three hours and 35 minutes.

Federer laboured at times in the contest, making 63 unforced errors, fighting hard to triumph in front of an empty crowd locked out by Paris' 9pm curfew, with the match finishing close to 1am.

The 20-time Grand Slam winner has played few tournaments over the past 18 months and conceded the physical toll the match took would make him assess his continuation at Roland Garros.

"We go through these matches, we analyse them highly and look on what's next and will do the same tonight and tomorrow, because I need to decide if I keep on playing or not or is it not too much risk at this moment to keep on pushing, or is this just a perfect way to just take a rest," Federer said at his post-match news conference.

"Because I don't have the week in between here and Halle like normal to see what's best now, if you count back from Wimbledon and so forth.

"It's just a lot going on, but having a match like this, knowing I could have probably played a fifth set but not knowing how I will wake up tomorrow is interesting, to say the least."

He added: "Every match here or Geneva, I have to reassess the situation after the match and see in the morning how I wake up and how the knee feels.

"From that stand point for me, it always goes like that… maybe even more so after a match like this that has been long. Like I explained before, I've not been two-three-and-a-half hour battles in practice either."

Federer's third round win sees him move into the last-16 where he is scheduled to play ninth seed Matteo Berrettini on Monday.