Grant Hackett was in hiding last night after another day of bizarre behaviour in which the troubled Olympian's family reported him as a "mentally disturbed" missing person.

Hackett was believed to have been holed up at the luxury Surfers Paradise Marriott hotel when police found him late yesterday after worried family and friends had scoured the Gold Coast for him.

His father Nev had described the 36-year-old as "definitely missing and definitely mentally disturbed" after Hackett failed to attend a private hospital and instead checked himself into the Palazzo Versace at Main Beach.

He vanished after hanging up on his father about 7.30am and his family later filed a police missing person report.

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The drama followed Hackett's arrest at his family's Mermaid Waters home on Wednesday after he flew into an uncontrollable rage believe to have been fuelled by alcohol.

Yesterday morning, he took to social media to allege his brother Craig had previously "beat the s..t out of me" and posted a photo of himself with a black eye.

"Everyone knows he is an angry man," Hackett said of Craig, who on Wednesday vented his family's frustrations at Grant's downward spiral.

A family member sought a court order following the altercation, which is believed to have left Grant in hospital.

After being reported missing, the triple Olympic gold medallist was found by police yesterday afternoon "alive and sober", his father said.

"He was found by police as a result of the media blitz," Mr Hackett, a former senior Gold Coast police officer, told The Courier-Mail.

"The police got a couple of calls and they located him and interviewed him. He's alive and sober but he's very, very embarrassed and doesn't want to see anybody or talk to anybody."

Mr Hackett said Grant had sent a text message to his mother Margaret to say "I'm okay but I can't talk".

Hackett senior pleaded with his troubled son to seek treatment for what he described on Wednesday as "mental health issues".

"He has been seeking help from a doctor for the last couple of months and was on the improve, but he's had a relapse," he said.

Mr Hackett said he hoped Grant would make contact and the family could heal its wounds.

"What happens now is up to Grant," he said.

"He has his own house but he's very, very welcome to come home. He's welcome in a lot of places. He's had so many offers of help but who knows what he's thinking at present?

"We just have to sit and wait and see what happens."

Mr Hackett said his son, who has entered rehab at least three times in recent years following a series of dramatic meltdowns, had been inundated with offers of more help and support.

"You wouldn't believe the people who have been offering to help Grant," he said.

"All I can say is Grant's had more support from everyone in the community than he ever had when he was winning gold medals at the Olympics.

"But in the long run, it's up to Grant. We can't force him to do anything."

Mr Hackett said his family had received legal advice not to comment on Grant's social media claims.

Friends last night were saying cracks were beginning to appear as early as New Year's Eve, with reports of an incident at Olympic champion Michael Phelps' wedding in the United States.

Things got worse with the breakdown of a relationship. After pleas from friends to help him on his return to the Gold Coast last month, his family tried to provide support.