Britain's Kyle Edmund was forced to retire from his US Open third-round match against Canadian teenager Denis Shapovalov because of a neck injury.
Shapovalov, 18, led 3-6 6-3 6-3 1-0 when the Briton pulled out.
Edmund, 22, was playing his 10th match in 14 days and had the trainer on three times before withdrawing.
More to follow.