Ian Thorpe in rehab
Swimmer Ian Thorpe of Australia speaks with reporters during a press conference near the Olympic Stadium in London on July 26, 2012 - by Gabriel Bouys
The 31-year-old, one of Australia's most recognised sportsmen, has struggled to adjust to life after swimming and with the disappointment of a failed effort to reach the 2012 London Olympics.
The Sydney Daily Telegraph said he was injured in a fall earlier this week before his family sought medical help, with Thorpe admitted to hospital on Wednesday, where he will be treated for depression and alcohol abuse.
Broadcaster Alan Jones is one of his closest associates and spoke to the swimming champion recently.
"Yes, it's serious but there's not a lot I can or want to add," Jones told the newspaper of the swimmer, who has also faced constant speculation about his sexuality.
"Ian is a beautiful person but he has difficulty recognising his problems."
Thorpe, who came out of retirement in 2011 in a bid to make the team for London but failed to qualify, released an autobiography in 2012 in which he admitted a struggle with depression and alcohol.
"Not even my family is aware that I've spent a lot of my life battling what I can only describe as crippling depression," he wrote.
"It's a terribly dark place in which to hide."
He added: "I suppose it was inevitable that I'd turn to other, artificial ways of managing my feelings, and I found alcohol."
Thorpe is Australia's most decorated Olympian with five gold medals at the 2000 Sydney and 2004 Athens Games, with his extraordinary success attributed partly to his abnormally large feet and hands.
He became the first person to win six gold medals at one world championships, in 2001, among 11 world titles overall -- along with 10 Commonwealth Games gold medals, six of them in Manchester in 2002.
But the demands of a celebrity lifestyle and grinding training sat uncomfortably with Thorpe and he quit in 2006, dabbling in jewellery design and television after his retirement, before the failed comeback.