Thorpe, who has been seen at social events over the New Year, including the Australian Open in Melbourne, has spoken of constant pain from an old back injury.
He released an autobiography last year in which he said he'd struggled with depression and alcohol abuse.
"Not even my family is aware that I've spent a lot of my life battling what I can only describe as crippling depression," the five-time Olympic gold medallist wrote.
He said he had also used alcohol as a way of dealing with hard times in his life.
A close friend of Thorpe told News Corp on Thursday night that they were thinking of the swimming legend.
"He had an accident at home," the friend said.
"He slipped and hurt himself.
"We're hoping he's going to be OK and make a full recovery."
Broadcaster Alan Jones, a close friend of Thorpe's, also said the swimmer had been going through some problems recently.
"Yes, it's serious but there's not a lot I can or want to add," Jones said on Thursday night.
"Ian is a beautiful person but he has difficulty recognising his problems."
- AAP
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