The 30-year-old reveals he lost interest in professional swimming after the 2008 Olympic Games in Beijing, China, where he scored another six gold medals, and considered walking away from the sport.

However, Phelps was encouraged to continue training, and although he was gearing up to head to the 2012 London Games, his heart was no longer in it.

"Leading into London, I didn't want anything to do with the sport," he told U.S. breakfast show Today. "I think I was just over it. Personally, I had a lot of struggle getting through the four years after '08. I just don't think I really knew what I wanted to do."

Phelps' lack of interest led to a blow-out fight with his longtime coach Bob Bowman and he didn't show up for practice for 10 days as the start of the London Olympics loomed.

Despite his lack of enthusiasm, Phelps added six more medals to his mantle, including four gold, but as his professional career appeared to be going from strength to strength, his personal life was spinning out of control, resulting in an arrest for driving under the influence in 2014.

"I sent myself down a downward spiral," he continued. "I think it was a sign more than anything else, that I had to get something under control, whatever it was. I look back at that night and everything happened for a reason."

Phelps believes his run-in with the law - his second alcohol-related arrest in 10 years - was a cry for help: "Honestly, at one point, I felt like I didn't want to see another day," he added. "I felt like it should be over."

He subsequently checked himself into Arizona's The Meadows rehabilitation centre for 45 days of treatment, but despite his penchant for booze, Phelps does not consider himself to be an alcoholic.

"I don't know (if I am an alcoholic)," he said. "I know I have moments where I have gone off the deep end where I shouldn't, and I would say (I've) binged more than anything else."

Asked if he believes he has a drinking problem, he defiantly stated, "No, because you can put a beer in front of me, or an alcoholic drink in front of me, and I won't feel the urge to drink it."

Now, Phelps insists he is a changed man and he is focused on success at the 2016 Summer Games in Rio de Janeiro, Brazil - his fifth and final Olympic Games.

"I want to be here," he said. "That's the difference. I had no desire to go work out before. I wanna retire how I wanna retire and I have a great opportunity to do that. I haven't trained like this in... a decade."

Phelps has also turned his personal life around and is set welcome his first child with fiancee Nicole Johnson imminently.