Robin Gibb is recovering in hospital after a blood transfusion.
The Bee Gees star was in an unnamed medical facility yesterday after undergoing the procedure, part of his continuing recovery from colon and liver cancer.
The 62-year-old singer had been due at a London fundraiser for a memorial to the RAF's Bomber Command, but had to cancel to go to hospital.
A source told The Sun newspaper: "Robin had an operation about three weeks ago and this was a follow-up. He is due to be signed out again shortly."
Robin has made a miracle recovery after undergoing seven rounds of chemotherapy since he was diagnosed 18 months ago, but also said he wonders if his family tragedies - including the deaths of his brothers Andy in 1988 and Maurice in 2003 - are a "karmic price" for the band's worldwide success.
He said: "I sometimes wonder if all the tragedies my family has suffered, like Andy and Maurice dying so young and everything that's happened to me recently, is a kind of karmic price we are paying for all the fame and fortune we've had.
"But we've worked hard for everything we've achieved.
"I am not and never have been at death's door. But the illness, and the untimely death of my brothers, has made me conscious of the fact that - rather than just think about it - it's crucial that you do today what you want to do."
Robin - who also has a sister Lesley and brother and fellow Bee Gee member Barry - also admits the death of his twin, Maurice, from complications resulting from a twisted intestine, is something he will never recover from.
He said: "How did I get over Maurice's death? I didn't. And I never will. I just don't accept it. I tell myself he's away on a long holiday and that we'll be seeing each other again soon."