"But Robin is a strong character, he is a fighter and has been encouraged by all the online messages from his fans.
"Dwina is doing everything possible and hasn't left his side."
Robin was treated for an inflamed colon in October after being taken to hospital complaining of "severe" abdominal pains, but said he was "determined" to overcome his health problems.
Friends added they are frustrated by Robin's condition as the clean living star "doesn't drink, eats well and exercises daily".
In a previously recorded interview to be broadcast this week on Sky Arts show Living The Life, Robin also tells of his inability to come to terms with the death of his twin brother, Maurice, in 1998 from a blocked intestine.
He describes his passing as "something I haven't accepted," adding: "I just imagine he is out there somewhere and I will bump into him one day."
Robin has also recently had to pull out of a number of scheduled engagements - including a Remembrance Sunday edition of the BBC's Songs of Praise, where he was due to perform the official Poppy Appeal song - because of his health.
- BANG! Showbiz