James Erskine said the five-time gold medalist is being treated for depression at a rehabilitation clinic, the Australian Broadcasting Corp. reported.
Residents of the street on which Thorpe's parents live called police after he tried to get into a vehicle he thought belonged to a friend, Erskine said.
Police recognized Thorpe and called an ambulance, the manager said.
The hospital where Thorpe was taken "more than suggested" he be taken to a clinic to be treated for depression, Erskine said.
Thorpe had not been drinking, the manager said, but antidepressants were found in his system. Thorpe also had been taking painkillers following shoulder surgery last week.
Thorpe, 31, released an autobiography last year in which he admitted to battling alcohol abuse and depression.