Grant Hackett's father has announced that his son is missing.
“I would think that if anybody has seen him to contact media or the police or the Hackett family,” his father Nev said.
"He's definitely a missing person. He's mentally disturbed and needs urgent help. His doctor can't find him, he hasn't kept an appointment with his lawyer," he continued.
"When we spoke to him several hours, he just hung up when we asked him where he was. We're extremely worried about him. Grant, let us know where you are, we love you, and we want to help you."
Just hours earlier, Hackett shared a bruised and bloodied photo to Instagram, claiming his brother had beat him.
The former Olympic swimmer was arrested yesterday after witnesses say he was was "going off" and stabbing a knife into a chopping block.
He was later released without charge.
Australian Olympic Committee president John Coates released a statement regarding Hackett's recent behaviour.
"We are concerned for Grant's welfare," he said.
"Grant is a great Olympic champion, one of the greatest swimmers of all time, and his contribution to the Olympic Movement and to sport in general should not be forgotten.
"He inspired many young Australian children to get involved in swimming. We hope he can overcome his current challenges and we have offered him any support he needs."