Robin Williams reportedly feared his Parkinson's Disease would prevent him from cycling.

The 53-year-old star - who committed suicide last week - turned to the sport to help him kick his previous drug and alcohol addiction but sunk into depression when the degenerative nervous disorder threatened his chances of being able to carry on riding.

Robin's close friend, Tony Tom, told The Sun newspaper: ''It [Parkinson's Disease] would have affected his ability to ride, no doubt.

''He could have turned back to his earlier vices if he wasn't riding and maybe that was one of the things he was thinking about.''

The 'Mrs. Doubtfire' star's wife Susan Schneider revealed earlier this week her husband was in the ''early stages'' of Parkinson's Disease, but he didn't feel ready to speak about his illness publicly at the time.

Robin was found dead at his home in Tiburon, California, on Monday (11.08.14) with a belt pulled around his neck and ''acute, superficial cuts'' on the inside of his left wrist.

Chemical substances were also found in his system during an autopsy, but toxicology results will not be made available for approximately two to six weeks, so further tests can be carried out.

Robin leaves behind his three children, Zak, 31, Zelda, 25, and Cody, 22, from two previous relationships.