Nick Kyrgios was forced to retire injured from the Aegon Championships at Queen's - less than two weeks before the start of Wimbledon.
Kyrgios took a nasty fall in his opening match against American Donald Young and, while able temporarily to continue, the Australian pulled out after losing a first-set tie-break 7-3.
The world number 20 appeared to be clutching his left hip and his subsequent withdrawal will be a particular concern with Wimbledon beginning on July 3.
The score was 4-4, 15-0 to Young when Kyrgios slipped on the baseline and his instant reaction was to put his face in his hands while lying with his back on the grass.
A medical time-out followed at the next change of ends but the 22-year-old signalled his ongoing discomfort with numerous shakes of his head.
The courts at Queen's Club do tend to be greener at this point in the summer, with Andy Murray and Nicolas Mahut both voicing disapproval last year after taking tumbles during their first round encounter. Two games after Kyrgios' slip, a ball girl also lost her footing on Centre Court.
Kyrgios' unexpected exit means Young goes through to face either Viktor Troicki or Janko Tipsarevic in the second round.
Earlier, fifth seed Jo-Wilfried Tsonga bounced back from his first-round defeat at the French Open last month by cruising past compatriot Adrian Mannarino 6-2 6-2.
Tsonga will play either Nikoloz Basilashvili or Gilles Muller in round two. Murray, who begins against Aljaz Bedene on Tuesday, is his potential opponent in the quarter-finals.