The 28-year-old swimmer is due to make his competitive return at the Arena Grand Prix in Mesa, Arizona next week, as he sets his sights on an Olympic return at Rio 2016.

In November, rumours of a Phelps comeback were fuelled when he re-registered with the United States Anti-Doping Agency.

He has had to wait six months before being eligible to compete.

American Phelps had ended his swimming career at the London 2012 Olympics, where he won four gold and two silver medals.

He eclipsed the record seven gold of countryman Mark Spitz, set in Munich 1972, when he powered his way to an unprecedented eight gold in the pool in Beijing 2008.

Together with his six Athens 2004 gold medals, his 18 gold - and 22 medals in total - make him easily the most decorated Olympian in history.

With 18 Olympic gold medals to his name, including four from London 2012, Michael Phelps is the most decorated Olympian of all time ©Getty Images



His return to the pool opens the possibility of him adding to that haul in Rio.

After London 2012, Phelps had insisted there was no prospect of him returning to competitive action.

He even joked that if he was to compete at Rio 2016, it would be in golf rather than swimming.

The Arena Grand Prix in Mesa, the fourth stop of USA Swimming's 2013-2014 Arena Grand Prix Series, is also set to attract fellow Olympians Ryan Lochte and Katie Ledecky in what USA Swimming is calling a "star-studded field".

More than 500 swimmers will take to the pool in the competition, which is scheduled to take place from from April 24 to 26.