Roger Federer asked for a medical timeout against No.33 seed Philipp Kohlschreibe to send shockwaves through the US Open.
The 36-year-old missed six months of tennis last year due to injury and caused some concern when he had to get a quick massage from a trainer after the second set.
But it didn’t halt his assault as he capped a 6-4 6-2 7-5 victory.
“It was more precaution. It’s all good. No problems there,” Federer said.
“I’m not worried about it.”
Federer now faces Juan Martin del Potro in the quarter finals who he has beaten 16 of 21 times the pair have met.