Emma Raducanu suffered an injury scare just four days before the French Open begins as the Briton lost to Danielle Collins in Strasbourg.
The 22-year-old produced an excellent first set but needed treatment on a lower back issue after falling 5-0 behind in the second.
Seemingly uninhibited by the problem on her return, Raducanu came back from a break down in the decider - but Collins rallied again to win 4-6 6-1 6-3 and reach the quarter-finals.
Raducanu had taken a wildcard into the clay-court event in Strasbourg to get more practice on the surface before the French Open starts on Sunday.
Despite the off-court medical timeout there appeared to be no obvious signs of discomfort for Raducanu, who put Collins under sustained pressure before the American pulled away.
Collins, a former Australian Open runner-up who beat Roland Garros champion Iga Swiatek in Italy last week, plays American top seed Jessica Pegula or Russian world number 30 Anna Kalinskaya in the last eight.
Raducanu said she was building a relationship with clay courts after her impressive opening win over Daria Kastakina on Monday.
Victory over world number 17 Kasatkina came after Raducanu's run to the Italian Open fourth round, where she won three consecutive clay-court matches for the first time in her career.
