Jack Draper was forced to retire in the second set of his fourth-round clash with Carlos Alcaraz at the BNP Paribas Open in Indian Wells.
The 21-year-old Briton was ultimately overcome by an abdominal injury he picked up during his previous match against Andy Murray.
He went shot-for-shot with the Spanish world number two in the early stages, but noticeably lagged as the first set went on.
Draper’s serve and movement suffered as Alcaraz ran away with the opener 6-2.
Some treatment from the physio in-between sets did little to improve his condition, and the world number 43 was only able to last two games in the second set before retiring.
The result means Alcaraz moves within three wins of regaining the world number one ranking.
“I was doing further damage, so there was no point in making it worse,” the 21-year-old told BBC Sport.
“At the end of my match against Andy [Murray, on Monday], I obviously had a bit of hip pain but my ab towards the end was getting sorer.
“I woke up [on Tuesday] and my ab was sore and when I started serving 100 per cent in the match it gradually got worse. I couldn’t really play properly.”
He added: “I’m at the start of properly working hard on my fitness training.
“I’ve done a lot of stuff on court over the years but I’ve never really worked truly on my body.
“I’m still early in my development. I’m starting to play grand slams with five sets. The physical nature of this sport is very demanding and so you’ve got to have a really resilient body to cope with the demands of the tour.”