World number two Daniil Medvedev lost at the Geneva Open on Tuesday in his first match after a hernia operation, leaving him short of practice ahead of next week's French Open.
The US Open champion, back on the tour after surgery, was beaten 6-2, 7-6 (7/5) by French veteran Richard Gasquet in the round of 16.
Medvedev underwent surgery last month after losing in the quarter-finals in Miami, missing the early clay-court season.
Geneva is a warm-up event ahead of Roland-Garros but Medvedev will have to go into the second Grand Slam of the year short of match time on clay.
It was the first time 35-year-old Gasquet had defeated a top two player since beating Roger Federer in 2005 — his only other victory over a top-two opponent in 38 attempts.
World number 75 Gasquet faces either Italian qualifier Marco Cecchinato or Poland's Kamil Majchrzak in the quarter-finals.
Last year's Geneva winner Casper Ruud, runner-up Denis Shapovalov and Reilly Opelka are the other top 20 players still in the Geneva draw.
