Reigning champion Ronnie O'Sullivan kept his title challenge on track with a comfortable 6-2 win over Thailand's Noppon Saengkham.
But O'Sullivan said he was struggling with "a really, really bad foot".
"I hope I am OK to play," the 43-year-old seven-time UK champion told BBC Sport. "It's an old running injury.
"I couldn't stop running forever so I got back to running four or five weeks ago and it's just really sore. I have to manage it. I don't want to pull out so will just have to run on the days I am not playing."
O'Sullivan grimaced on a couple of occasions, but it did not seem to affect him despite not being at his fluent best in beating his Thai opponent in a match almost devoid of safety play.
O'Sullivan will face Ding Junhui in the next round.