George Michael has suffered a series of medical problems since 2011.
The singer, 50, has been out of the spotlight since last year, when he fell out of a car on the M1 motorway and was airlifted to hospital with a head injury.
In 2011 he suffered severe pneumonia which left him temporarily in a coma and meant he needed to undergo a tracheotomy in order to breathe.
He has also battled depression and drug addiction.
More top news
Tech giants Facebook and Google both have simple, powerful tools to help friends and family keep track of loved ones
At least 2,000 people took to the streets of Baltimore yesterday to demand answers over the death in custody of Freddie Gray
The London Marathon brings together thousands of people raising money for charity - not to mention some rather unusual costumes.