The world's most successful Olympian, Michael Phelps, is set to come out of retirement and compete at a domestic meeting in the United States next week.

USA Swimming announced on its website that Phelps is due to race at the Arena Grand Prix in Mesa, Arizona, which runs from April 24-26.

The USA Swimming report stated: "A record-setting 22-time Olympic Games medallist, Phelps is expected to swim competitively for the first time since winning six medals, four of them gold, at the 2012 London Olympic Games."

Phelps, now 28, won 18 Olympic gold medals - six in Athens, eight in Beijing and four in London.

Phelps, from Baltimore in the United States, had given no indication he could be tempted back into the water when he signed off from the London Olympics.

On retiring, he said: ''I don't want to swim after I turn 30 and that is in three years, and I don't want to swim for another three years.

''I would be past 30 by the time of the next Olympics. I have achieved what I wanted to achieve, Bob (coach Bob Bowman) and I have somehow been able to do every single thing.

"'If you can say that about your career then it's time to move forward, time to move on to other things.

''I finished my career how I wanted to."

Speaking to Press Association Sport in July 2013, as speculation began to swirl about a comeback, Phelps said: ''If anybody would know about me coming back it would be myself, and I haven't said one thing to anybody about anything.

''I enjoy playing golf, I enjoy waking up at noon every day - it's a good life."

Yet it was confirmed last November that Phelps had re-registered with the United States Anti-Doping Agency, allowing drug testing to resume and him to move closer to a potential return, possibly with a view to competing in the Rio de Janeiro Olympics in two years' time.

Coach Bowman said last month: "He looks like he is definitely in shape.

"If he swims a meet in the next couple months and does well, he will probably give it a shot in Irvine (at the United States Championships). But he doesn't have to do that to have a shot at the 2016 Olympics."