Thorpe announced his retirement last November

The allegations about the five-time Olympic champion, who retired last year, came from French paper L'Equipe.

The sport's world governing body FINA has lodged an appeal with the Court of Arbitration for Sport on a doping test without naming the athlete concerned.

Swimming Australia's Glenn Tasker said: "I will support Ian 1000 per cent."

News Conference: Swimming Australia's Glenn Tasker

The organisation's executive director said Thorpe felt he was "hit by a lightning bolt" when he first saw the report on Saturday.

"Those people who know Ian will know that whatever this finding is there will be a reason for it but I know Ian is vehemently opposed to any sort of performance-enhancing drug," Tasker added.

"He is a young man of unbelievably strong principles and integrity and I've known him for a long time.

"All these things have a backlash effect. At this minute there isn't a positive test, it's an adverse finding.

Until solid evidence to the contrary is produced, Ian Thorpe remains a great Australian champion Australian PM John Howard

"Hopefully reasonable-thinking people will accept that for what it is and they won't be hanging anyone until the judge has made his decision.

"If it is Ian Thorpe, then somebody has leaked that information, his privacy has been grossly invaded and it's not good for that athlete, but it's not good for any athlete around the world."

Jacco Verhaeren, the coach of Thorpe's rival Pieter van den Hoogenband, said he was angry that a test result, that had not been positive, had been leaked to the media.

"This is damaging somebody's career without any reason and I think that's the worst about it," he said.

"I think there are people to investigate these kinds of things and I think we should first listen to these people before damaging somebody who is an exceptional sportsman and to me a very honest guy. To me he is not under suspicion."

Australian prime minister John Howard said: "I don't intend to react to, let alone endorse, unsubstantiated allegations in a French newspaper. As far as I'm concerned, until solid evidence to the contrary is produced, Ian Thorpe remains a great Australian champion."