Seventh seed Hubert Hurkacz arrived at Wimbledon as a dark horse but became the third men's top-eight player to make an early exit as he retired from his second-round clash against Frenchman Arthur Fils with a knee injury on Thursday.
Having made a slow start, Hurkacz was on course to level the match at two sets apiece when he dived for a volley at the net in the fourth set tiebreak to go 8-7 up, but landed badly and immediately clutched his right knee.
He limped on after a lengthy medical timeout, but was forced to throw in the towel at 7-6(2) 6-4 2-6 6-6 having gone down 9-8 in the tiebreak.
"It's tough to win a match like this against a friend. We were playing super good in the fourth set. We had some great points. He was jumping everywhere," said Fils.
"I'm really sorry for him. I hope he will recover quickly."
Elsewhere, Frenchman Gael Monfils, 37, sealed a hard-fought 7-6(5) 6-4 7-6(3) win over three-times Grand Slam champion Stan Wawrinka, while Australian ninth seed Alex de Minaur secured a 6-2 6-2 7-5 win over Spaniard Jaume Munar.
In the women's competition, former world number two Paula Badosa eased past Czech Brenda Fruhvirtova 6-4 6-2 to move into the third round as Ukrainian 18th seed Marta Kostyuk produced a fine comeback to beat Australian Daria Saville 4-6 7-6(2) 6-4.
American 12th seed Madison Keys made light work of China's Wang Yafan, winning 6-2 6-2 to advance to the last 32, while Russian 14th seed Daria Kasatkina outclassed Britain's Yuriko Miyazaki 6-0 6-0.