Double amputee Oscar Pistorius should be allowed to race in the Olympics, three US former champions said Thursday, but things might change if the South African begins to post super-fast times.

Pistorius will become the first double amputee athlete to compete at an able-bodied Olympics when he lines up in the men's 400m. He will also race in the 4x400m relay.

The 25-year-old, known as 'Blade Runner' because he runs with carbon fibre prosthetic running blades, has not been universally welcome with some observers believing he has an unfair advantage.

Pistorius, who will also defend his titles in the 100m, 200m and 400m at the Paralympics next month, has a personal best time of 45.07sec in the 400m, something that means he should be running, according to Edwin Moses.

"I think Oscar should be able to run," the former 400m hurdler said. "He's one of the few who've proven he runs world-class times.

"It's a great story, a great inspirational story, it's what sport's all about. But if he starts running 41.6sec, the question's going to be asked again."

The 2000 Sydney Games 100m gold medallist Maurice Greene agreed, saying: "We created the Paralympics to give people with disabilities a chance to get out there and compete because they can't compete with us (able-bodied athletes).

"But on the flipside, if you're able to compete with us, why not?"

High jump legend Dick Fosbury, who gave his name to the "flop" approach to the bar after revolutionising the event, added that the question of whether Pistorius got an advantage from his prosthetic blades was a question for the "federations".

"I tend to agree (with him running)," Fosbury said. "Sport is sport, and we all appreciate other athletes that are trying to become better athletes, better persons overall.

"Of course, it's a challenge to define what the boundaries are and determine whether he or any athlete has an advantage with the device. But that's up to our federations to study that very carefully and determine whether that's equal.

"I think in his case, he's a good person, a good competitor. This is a great show, it's a great story."

The Johannesburg-born runner had both legs amputated below the knee when he was 11 months old because of a congenital condition that meant he was born without fibulae -- lower leg bones.

This hardly hindered his sports activity when he grew up and performed with prostheses.

At first, Pistorius played contact sports at school, but when the sportsman fractured a knee playing rugby he took to track running, and has never looked back.

He was cleared four years ago to run against able-bodied athletes when the Court of Arbitration for Sport (CAS) overturned a ruling by the International Association of Athletics Federations (IAAF) that his blades gave him an unfair advantage.

Pistorius hired experts to do tests that proved the blades did the same work as normal feet.

The 25-year-old went on to win a silver medal as part of the 4x400m relay team at the 2011 World Championships in Daegu, South Korea.