Chad le Clos, one of the few men to have beaten Michael Phelps at the Olympic Games, has thrown down the challenge to his old rival, urging him to get back into training so they can have a rematch at Rio in 2016.

The South African pulled one of the biggest upsets of the 2012 London Olympic Games when he got his hands on the wall ahead of Phelps after a dog fight to win the gold medal in the 200 meters butterfly.

When Phelps retired after London, Le Clos easily won the 100 meters and 200 meters butterfly double at last year's World Championships, but the prospect of another showdown with the greatest swimmer of all time has got him excited.

"I really, really hope that he and his team decide to swim in Rio, I really believe it will be great," Le Clos said Friday. "It's added motivation for me ... with Michael back, it's really sparked my fire, so to speak."

Phelps and Le Clos had another ferocious battle in London, with the American coming out on top in the 100m butterfly, an event he has won at three successive Olympic Games.

But the 22-year-old Le Clos has been working hard on his speed since then to avenge that loss and believes he can not only win both events next time, but can also break both world records, currently held by Phelps.

"I believe by Rio, I should be in peak condition," said Le Clos, currently in Singapore for the final round of swimming's annual World Cup series. "I don't think he will be worse in Rio, I think he'll be back where he wants to be."

Phelps returned to swimming last year and quickly set about making up for lost time, suggesting he was on course for Rio.

He qualified for the US team for next year's world championships in Russia but lost his place and was suspended for six months by US swimming after being arrested for drunken driving.

He is currently undergoing treatment and is not certain of making it to Rio though few doubt he will be on the blocks in Brazil, looking to add to his record tally of 18 golds.