Former Australian swimming great Hackett in rehab
Australia's Grant Hackett pictured after competing in the men's 1,500m freestyle at the FINA World Championships in Melbourne on April 1, 2007 - by Torsten Blackwood
Hackett, who won the 1,500m freestyle at both the 2000 and 2004 Olympics and claimed four world titles in a dominant decade at the top, jetted to the United States on Tuesday, apparently to begin rehabilitation.
It comes just weeks after fellow Australian swimming star Ian Thorpe began treatment for depression after a mixture of painkillers and anti-depressants left him disoriented on a Sydney street.
"Grant is currently in transit to seek treatment for a dependency to Stilnox medication," his manager Chris White said in a statement.
"His family and friends are enormously proud of his courage in pursuing this course of action."
Stilnox is a drug used to treat insomnia, with athletes sometimes prescribed it if they are having trouble sleeping before big events, although it was banned by the Australian Olympic Committee just before the 2012 London Games.
- 'In denial' -
However, on arrival in Los Angeles, Hackett told waiting Australian media that he was in the United States for a "retreat".
"No, I'm not calling this rehab whatsoever," he said. "This is a retreat, to get away for a while, to recharge the batteries which I have been planning for some time."
His father Neville said his son was "in denial".
"I think Grant is a little bit in denial, he thinks he just needs a bit of a recharge and a rest," Neville Hackett told Sydney radio station Triple M.
"I'd say rehab is certainly something that's needed there."
He added that his son would not be able to "fool the experts for long", saying that family had organised the treatment for him.
"We got onto the best experts we could who were available. They suggested the US after two meetings we had, and that's how it's all come about," he said.
"We weren't about to tell the world about this, of course, because we consider it a private family matter, but Grant being who he is, it's all over the media."
Asked what the main issue was, he replied: "I would suspect Stilnox but I can't be a 100 percent sure and that is why we have taken that action we've taken."
Hackett's departure from Australia came just days after he was photographed in the early hours with only a singlet around his waist in the foyer of a Melbourne hotel, searching anxiously for his four-year-old son.
The former great, 33, retired from the pool in 2008 and has worked for the Nine Network and Westpac Bank since then.
But his reputation took a huge hit after he trashed his apartment in an alcohol-fuelled rampage in 2011 that saw his wife Candice Alley leave him. They have two young children.
His father said that since then his son had suffered "two years of hell, living by himself, working hard".
The lanky Queenslander burst onto the scene at the 1998 world championships in Perth as a 17-year-old, where he lost the 400m final to a 15-year-old Thorpe.
The pair went on to help Australia's swimming team to the nation's best run of success since the golden days of the late 1950s and early 1960s.