Brendan Grace is receiving treatment for cancer, a spokesperson for the comedian has said.
Speaking to the Irish Daily Mirror, the spokesperson said: "Brendan Grace has been in hospital for the last four weeks receiving treatment for pneumonia.
"It has now transpired that he is also suffering from cancer for which he is receiving ongoing care and treatment.
"His family are a great support to him at this difficult time and respect for their privacy would be much appreciated."
"His current July/August Irish Tour has been cancelled," the spokesperson added.
"Brendan is still in hospital and will be remaining there for ongoing treatment. He is hospitalised in Ireland."
68-year-old Dubliner Grace lives in the US but regularly returns home to tour. He has battled a number of health issues in recent years including a stroke and complications from diabetes.
A showbusiness veteran for 50 years, Brendan Grace began his career in music before turning to comedy.
Along with his standup show, he is best known for his unforgettable cameo as Father Fintan Stack in Father Ted.