Marseille - Stan Wawrinka's troubled comeback from a six-month injury lay-off suffered another setback on Thursday when he was forced to quit his second-round match in Marseille against world No 193 Ilya Ivashka of Belarus.
The 32-year-old Wawrinka, the winner of three Grand Slam titles, was 6-4, 1-1 down to the qualifier when he retired.
Swiss star Wawrinka, now down at No 13 in the rankings, missed the last six months of the 2017 season after undergoing knee surgery.
He has endured a traumatic start to 2018, losing in the second round of the Australian Open to unheralded Tennys Sandgren of the United States.
After making the semi-finals in Sofia, he then slumped to an embarrassing defeat to Dutch world No 259 Tallon Griekspoor in Rotterdam last week.
ATP Marseille Open results on Thursday (x denotes seeding):
Karen Khachanov (RUS x9) bt Mischa Zverev (GER) 6-2, 6-1
Tomas Berdych (CZE x4) bt Stefano Travaglia (ITA) 5-7, 7-6 (7/4), 6-3
Filip Krajinovic (SRB x8) bt Gilles Simon (FRA) 6-3, 6-3
Nicolas Mahut (FRA) bt Gilles Muller (LUX x6) 3-6, 6-2, 6-4
Ilya Ivashka (BLR) bt Stan Wawrinka (SUI x2) 6-4, 1-1 - retired