George Michael, 53, was found dead by his partner on Christmas Day. Picture: AP

Michael, 53, was discovered in bed at his home in Goring-on-Thames, Oxfordshire, by his partner Fadi Fawaz on Christmas Day.

Michael was discovered in bed by his partner Fadi Fawaz. Picture: SuppliedSource:Twitter

Thames Valley Police, who carried out the post-mortem, said in a statement: “The cause of death is inconclusive and further tests will now be carried out. The results of these tests are unlikely to be known for several weeks. Thames Valley Police will prepare a file for the Oxfordshire Coroner.

“Mr Michael’s death is still being treated as unexplained but not suspicious.”

Reps for Michael initially attributed his death to a heart attack. Shortly after his death Michael’s long-time manager Michael Lippman told Billboard he died of heart failure.

Tributes of flowers are left outside Michael’s London home. Picture: Jack Taylor/Getty ImagesSource:Getty Images

“I’m devastated,” he said. “(There was) no foul play whatsoever.”

However, it was known that the star was caught in a struggle with drugs in the years before he died and in a few photos taken only months before his death at an Oxfordshire restaurant he looked bloated and was said to have appeared tired.

Fans gather in front of George Michael's home in the village of Goring. Picture: AFPSource:AFP

There have also been reports he had been suffering from a lung condition ever since he contracted pneumonia in 2011. At the time, doctors were forced to perform a tracheotomy on the singer to keep his airways open.

The post-mortem result came as it was reported that his friend and fellow musician Elton John is set to sing at Michael’s funeral while a tribute concert held in his name is being planned by his celebrity friends.

Details of his funeral have not yet been revealed but there are reports that John is planning to perform the pair’s 1991 duet Don’t Let The Sun Go Down On Me.

Elton John is reportedly set to sing at Michael’s funeral. Picture: AFPSource:AFP

Music stars are also said to be considering a tribute concert in honour of the singer.

Michael, who was born Georgios Kyriacos Panayiotou in north London, sold more than 100 million albums throughout a career spanning almost four decades.

He first found fame with schoolfriend Andrew Ridgeley in duo Wham! in the 1980s before forging a successful solo career.

However, while largely retreating from public life in the last decade his life over this period was dogged by health scares and rumours of drug problems.

Last year he publicly denied new allegations about drug-taking, describing them as ‘‘highly inaccurate”.

He nearly died from his pneumonia bout in late 2011 and after receiving treatment in a Vienna hospital made a tearful appearance outside his London home telling the media it had been ‘‘touch and go” whether he lived.

The news comes as Michael has made a return to Britain’s record charts following his death, the Official Charts Company said on Friday.

“Last Christmas”, one of his best-selling singles from his time in the pop duo Wham!, has climbed to number seven in the charts -- its first time in the top 10 sales since it was released 31 years ago.

George Michael in 1987. Picture: Michael Putland/Getty ImagesSource:Supplied

The song has also become the second most streamed track of the week, with 3.6 million streams.

Michael’s greatest hits collection “Ladies & Gentlemen” has seen a stagging 5,625 percent surge in combined sales and streams over the past week.

The album, which topped the charts for eight weeks when it was released in 1998, is now at number eight.

“The Final”, Michael’s last album with Wham!, came in at 40 followed by “Twenty Five” at 47, “Faith” at 62, “Symphonica” at 73 and “Older” at 84.

“The sudden and terribly sad death of George Michael has naturally prompted his fans to re-explore his rich catalogue again,” Martin Talbot, chief executive of the Official Charts Company, said in a statement.

“Quite appropriately, given the season, it is ‘Last Christmas’ which makes the biggest impact,” he said.

Michael sold more than 100 million albums in a career spanning more than three decades but in recent years he became better known for a series of bizarre episodes, some of them linked to drug use.

His last album “Symphonica” came out in 2014 and topped the UK Albums Chart but his last album before that -- “Patience” -- was in 2004.dt/har