Tom Petty's cause of death has been "deferred".
The 66-year-old music legend passed away last week after being rushed to hospital following a cardiac arrest but after the autopsy was completed, "it was clear further tests needed to be done," according to The Blast.
One day after his cardiac arrest, Petty's agent Tony Dimitriades revealed he passed away when his family agreed to switch off his life support after learning he had no brain activity.
Petty was surrounded by his friends, family and his bandmates at UCLA hospital in Santa Monica, California, when he died.
Tributes from fellow musicians and fans poured in after they learnt that the American Girl hitmaker was fighting for life in hospital and among them was Kings of Leon rocker Nathan Followill, who said he'd struggle to perform after hearing the news.
He wrote: "Tom Petty was one of the biggest inspirations for me as a musician. This one will hurt for a long time. Truly one of the sweetest people on earth. Rest In Peace brother. It's going to be hard to take the stage tonight with such a heavy heart. Luckily music is what I use to get through tough times like these. Love one another."
Petty shot into the limelight in 1976 when he and his band the Heartbreakers dropped hits Don't Do Me Like That and Here Comes My Girl.
He also spent time in the supergroup The Traveling Wilburys - comprised also of Bob Dylan, Roy Orbison, George Harrison and Jeff Lynne - in the 1980s.