Defending world champion Mark Williams has revealed doctors are confident his health scare is not related to his heart after going to hospital suffering from chest pains.

The Welshman lost the opening session of his second-round match with David Gilbert 5-3 at the World Championship in Sheffield.

Later, Williams posted on Twitter that he was in the A&E department of a local hospital, saying: "Couldn't stick the chest pains no more."

The 44-year-old informed tournament officials of the issue after the session and was advised by the on-call doctor to attend hospital. Williams made his own way there and is understood to be with his wife Joanne and son Kian.

Williams posted an encouraging update during Friday evening.

"Doctors are confidant it's not anything to do with my heart," he tweeted. "Awaiting more tests at 10 o clock . #cantwaitformebed."

Breaks of 105, 66 and 58 had earlier helped Williams get back on level terms against Gilbert, but the latter took the last two frames of the day to carve out a 5-3 lead.

Their last-16 match is due to resume at 10am on Saturday at the Crucible.