A post-mortem examination carried out to determine the cause of George Michael's death has proved "inconclusive" and more tests are needed, UK police said.
Michael, 53, was discovered in bed at his home in Goring-on-Thames, Oxfordshire, by his partner Fadi Fawaz on Christmas Day.
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.
"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 died and in a few photo taken only months before his death at an Oxfordshire restaurant he looked bloated and was said to have appeared tired.
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.
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.