World number four Paul Hunter has been diagnosed with cancer of the colon.
Hunter still plans to play in Sheffield
The three-time Masters champion had been suffering from stomach pains for several months and recent tests revealed six cysts in his stomach.
He will undergo hospital treatment during the World Snooker Championship, which starts on 16 April, but still plans to play in the tournament.
The 26-year-old said he planned to be "tenacious and positive" in his fight against the disease.
"Paul will undergo treatment to cure himself of this illness," added a spokesman for the World Snooker Association.
Three years ago Hunter had surgery to remove a cyst on a testicle.
Snooker legend Jimmy White told BBC Sport his thoughts are with Hunter.
White, a six-time world championship runner-up, has rebuilt his career after recovering from testicular cancer.
"I just wish him and his family a speedy recovery," said White.
And seven-time world champion Stephen Hendry has also passed on his support.
"This is terrible news and the kind of news that puts things in perspective," said the Scot.
"It's the kind of thing that happens to other people, not one of your own.
"I'd just like to say on behalf of myself and all the other players and staff at my management company that we wish Paul a speedy and full recovery."