Olympic medallist swimmer Grant Hackett has left Australia for the US for a stint in rehab out of the spotlight, according to media reports.

Hackett made headlines after being photographed partially nude in the early hours of Saturday morning at Melbourne’s Crown hotel, searching for his four-year-old son.

It’s now emerged the former swimming star is seeking treatment for an addiction to prescription sleeping tablets.

“Grant is currently in transit to seek treatment for a dependency to Stilnox medication,” his manager Chris White told the Herald Sun newspaper.

“His family and friends are enormously proud of his courage in pursuing this course of action.”

News Limited websites report another witness to Hackett’s unusual behaviour has come forward, claiming he was seen in a state of semi-undress with a small child, either his son Jagger or Jagger’s twin sister Charlize, some hours before the previously-reported incident.