Australian wildcard Bernard Tomic pulled out of the US Open on Thursday with a left hip injury, handing fourth-seeded David Ferrer a third-round berth.
Tomic, 21, said he'd also been battling flu prior to his first round victory over Dustin Brown, and when the hip pain flared he opted to take a conservative approach.
"I don't want to muck around with that area. It's painful," said Tomic, who retired after the first set of his first round match at the Australian Open against Rafael Nadal in January and underwent double hip surgery shortly thereafter.
It's not a scenario Tomic wants to repeat - either the mid-match retirement or the aftermath.
"I can't afford to get on court and play against David and cause much more pain to myself, because I'm going to have to stay with him the whole match. For me, right now, I cannot do that," Tomic said.
"Who knows? I can potentially make it 10 times worse. For me, it's the best thing not to go on court today (Thursday). It's a very difficult decision for me, but I have to do this."
Tomic said it didn't feel like the same hip trouble that required surgery.
"It's a different area, that's all I can sort of say now," he said. "I'll get it seen with a specialist, so I get their ideas and I'll decide what's the best idea.
The latest setback casts doubt on Tomic's participation in Australia's Davis Cup World Group playoff against Uzbekistan on the grass courts of Perth's Cottesloe Tennis Club immediately after the US Open.
"For sure my biggest priority is to get this hip checked and see what the cause is and what problem it is," he said. "Then after that I can look into whether I can go down to Australia for the event in Perth for the Davis Cup."
Tomic has endured a troubled year since January, coming back from surgery to suffer a record 26-minute defeat in his return to competition at Miami.
He dropped out of the top 100 for the first time in three years after a second-round exit at Wimbledon, and in July global management company IMG said it had split with him, reportedly over concerns over his off-court behaviour.
But Tomic had been turning things around on court, lifting the trophy in Bogota to rise to 67th in the world.