George Michael was taken to hospital after collapsing at his home.
The 'Careless Whisper' hitmaker was treated by paramedics at his north London mansion for four hours on May 22 due to a mystery illness before being helped into an ambulance.
Shocked witnesses told The Sun newspaper that two emergency vehicles responded to a 999 call at about 8am and rushed to help the 50-year-old singer, who lives in Highgate in London.
The star was reportedly taken to hospital at 12pm for emergency treatment but his agent has refused to comment on why he suddenly collapsed and whether or not it was related to drugs.
A spokesman said: "George Michael was in hospital for routine tests but there is nothing further to say."
George almost died of pneumonia in 2011 and has had to deal with a number of health problems over the years, including depression and drug addiction, which has seen him arrested multiple times and he served an eight week prison term in 2010.
Last year, he was also airlifted to hospital after he fell out of a car on the M1 and was treated for "superficial cuts and bruises".
Regarding the recent incident, a London Ambulance Service spokesman said: "We were called just before 8am on May 22. We sent two ambulance crews and staff treated one patient, a man, who was then taken to hospital."
Meanwhile, earlier this year the former Wham! insisted he hadn't touched drugs for more than 18 months after smoking up to 25 joints a day.
He said: "I've completely stopped. I have decided to change my life and I haven't touched it for well over a year and half now."