The tenor was rushed to hospital in October after being taken ill while recording his new album.
However, he said he was worried about the operation after doctors warned that his condition would be "touch and go" when it was over.
He told GMTV: "I wasn't really that aware of what was going on... I was flitting in and out of consciousness. I remember hearing lots of medical people saying words like 'haemorrhage' and lots of very scary things."
The 41-year-old recently revealed that he plans to go ahead with his scheduled album release date because he believes his fans deserve it.
He will undergo a course of radiotherapy in the New Year.