Roger Federer says he may pull out of the French Open if there is too much risk to his knee, and to his Wimbledon prospects, if he plays on.
The Swiss beat Dominik Koepfer late on Saturday night over three-and-a-half hours in only his sixth match since having double knee surgery.
Federer, 39, is due to play Matteo Berrettini in the last 16 on Monday.
But he said he will decide later on Sunday whether now would be the "perfect time to take a rest".
The 20-time Grand Slam champion lacked fluency and trust in his game before coming through to beat Germany's Koepfer 7-6 (7-5) 6-7 (3-7) 7-6 (7-4) 7-5 at a near-empty Roland Garros.