THE autopsy on former American Idol contestant Michael Johns has been completed, but the US medical staff is reportedly deferring the cause of death pending toxicology results.

Perhaps more well known in America than his home country, news of the Perth-born 35-year-old's bizarre death shocked the US entertainment industry on the weekend.

TMZ reported the Perth crooner who made a name for himself on American Idol and died suddenly on the weekend, sprained his ankle last week with the swelling spread up to his knee.

He was cleared to go home, but the next afternoon was found in a friend's apartment on a couch unresponsive and when paramedics arrived he was dead.

Law enforcement sources told the US entertainment website that police were informed Johns had engaged in heavy alcohol use at some point prior to his death.

It was earlier suggested that a possible blood clot from the ankle injury, or deep vein thrombosis, could have been the cause of death.

But so far the US coroner has not concluded that.

The fact that toxicology tests are being performed suggests the coroner wants to know if alcohol and/or drugs played a part in Johns' death.

"Our family is devastated by the passing of our beloved Michael, a wonderful husband, son, brother, uncle and friend," the singer's family said in a statement on Saturday.

"We appreciate the outpouring of love and support we have received from all corners of the globe.

"Please keep Michael in your thoughts and respect our need to grieve privately in this difficult time."

Johns finished eighth on American Idol in 2008 despite controversy.

It was revealed he had signed with Madonna's Maverick label in 2002, something some believed should rule him out of the show because it was designed to unearth unknown talent.

"His acoustic version of the Bee Gees' T o Love Somebody was very special, but I will always remember him singing The Beatles' You Never Give Me Your Money/Golden Slumbers," American Idol executive producer Nigel Lythgoe told USA Today.

American Idol judge Simon Cowell, who would destroy young singers with his harsh critiques, was full of praise for Johns when he auditioned for the show aged 28 — the final year he was eligible.