Jack Draper's fitness issues plagued him once again as he was forced to retire in his second-round Winston-Salem Open match against Dutch second seed Tallon Griekspoor on Tuesday.
Griekspoor had edged a closely-fought first set 7-6[8] before Draper - who missed Wimbledon due to a serious shoulder injury - called it quits.
The 21-year-old strolled past Nuno Borges in the first round - his first top-level match since the French Open - held his own against the world number 25 in an incredibly even first set, as neither man brought up a single break point.
Draper also recovered from a 2-0 deficit in the first-leg tie-breaker to lead on four occasions, but with the Briton 8-7 to the good, Griekspoor took the next three points on the bounce to take the opener before Draper decided that he could not go on.
The world number 118's withdrawal has sparked fears over his participation in the US Open - which begins on Monday - and both Harriet Dart and Heather Watson began their bids to qualify for the main draw of the Grand Slam on Tuesday.
Dart came from a set down to defeat France's Chloe Paquet 3-6 6-4 6-1 in the first preliminary round, but Watson's run came to a swift end with a 3-6 2-6 loss to Ukraine's Dayana Yastremska.
