British athletics star Dwain Chambers has admitted testing positive for a banned drug but denied knowingly taking it.
His lawyer said the sprinter had failed an out-of-competition test for the banned steroid THG on 1 August.
A statement issued by Chambers said he was not guilty of "a wilful or calculated attempt on his behalf to deceive the authorities".
It added that in eight years in competition, Chambers has "never been tempted to succumb to illegal methods of performance enhancement".
Chambers faces a minimum two-year ban if the B test confirms the discovery in his urine sample of THG (tetrahydrogestrinone), a newly-discovered drug that is rocking the world of athletics.
Chambers' lawyer Graham Shear added that "the IAAF (athletics' governing body) and UK Athletics' procedure is still to provide any conclusive decision".
Under British Olympic Association rules, Chambers would also be barred from Olympic participation for life if found guilty of doping.
DOPE TEST PROCEDURE FOR OVERSEAS TESTS
Athlete's sample divided into two parts - A and B
If A sample tests positive, B sample sent for testing
If B positive, IAAF decide if there is a case to answer
If so, matter referred to athlete's national agency
(UK Athletics in UK)
Independent committee appointed by UK Athletics
Athlete presents defence to committee at closed hearing
Committee gives verdict - and sentence if athlete found guilty
Chambers' statement said that his trainer, Remi Korchemny, had instructed him to use as his nutritionist Victor Conte of Balco Laboratories - the company at the centre of the THG scandal.
It added that when Chambers heard of his positive test, he had challenged Conte, who had assured him "that all supplements given were within IAAF rules".
Chambers' lawyer added: "I understand that Mr Conte continues to deny that the supplements he prepared for my client and other athletes contain any illegal substances. This is a serious matter that the US authorities are investigating."
Lyn Davies, the president of UK Athletics and a former Olympic long jump champion, declined to comment directly about the Chambers case.
But he told the BBC: "UK Athletics is very vigilant and does everything possible to educate athletes and warn them [about the consequences of using drugs].
"But if you become Olympic champion or world champion today, it means that you become a millionaire.
"Obviously the motivations and the temptations are understandable - but it's very disappointing."
DWAIN CHAMBERS FACTFILE
European 100m champion
Joint GB 100m record holder with Linford Christie: 9.87secs
Won 100m bronze at 1999 World Championships
Disappointing 4th in 100m at 2003 Worlds in Paris
Another former Olympic champion, Lord Coe, a member of the IAAF council and deputy chairman of London's 2012 Olympic bid, admitted: "Some people will always keep trying to cheat.
"We have probably opened a can of worms but I would rather have that embarrassment than see the decline of the sport," he told BBC Radio Five Live.
Chambers' step-father, Lascell Golding said: "Dwain would never take drugs. They are talking about someone else.
"He is always careful about what he is doing. He wouldn't take anything for his cold unless he is 100% sure."
THG came to the attention of the athletics authorities when an anonymous coach turned in a used syringe containing the substance.
It was thought to be undetectable by normal dope tests.