Hackett, who has struggled with drug and alcohol problems away from the pool, was detained by Gold Coast police after suffering a "breakdown" at his parents' home, his father told local media.
The swimmer's brother Craig later told reporters that Hackett was a "danger to himself and to the community" and that his family was unable to help him alone.
On Thursday, Hackett posted a photo of himself on Instagram showing bruising around his eye and cuts on his face.
