A post-mortem examination into the cause of George Michael's death was "inconclusive" police have said.
The star died aged 53 on Christmas Day at his home in Goring-on-Thames, Oxfordshire.
More tests will now be carried out to determine what led to his death, Thames Valley Police said in a statement. The results of these tests are unlikely to be known for several weeks.
Michael's death is still being treated as unexplained but not suspicious.
The post-mortem examination took place on Thursday.
South Central Ambulance Service were called to Michael's property at 13:42 GMT on 25 December and the singer was confirmed dead at the scene. Thames Valley Police also attended.
Michael's partner Fadi Fawaz said he had found the singer lying "peacefully in bed".
He told The Daily Telegraph: "I went round there to wake him up and he was just gone. We don't know what happened yet."
Michael's manager, Michael Lippman, said the singer had died of heart failure.
Sir Elton John led tributes to Michael, describing him as "the kindest, most generous soul and a brilliant artist".
Former Wham! bandmate Andrew Ridgeley said he was "heartbroken at the loss of my beloved friend".
Madonna, Boy George, Ringo Starr and Robbie Williams also paid tribute to the singer, while bouquets of flowers were left outside his riverside home in Goring.
Fans have also been lighting candles and leaving handwritten cards outside his home in Highgate, north London.
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 Ridgeley in duo Wham! in the 1980s - reaching number one in the UK singles charts on four occasions.
He went on to forge a successful career as a solo artist, with hits including Careless Whisper, Outside, Fast Love and Jesus to a Child.