British Greco-Roman wrestler Myroslav Dykun has been suspended after testing positive for amphetamines, British Wrestling have confirmed.
The 29-year-old, originally from Ukraine, failed a test for the drug and is awaiting the outcome of a B sample.
"I can confirm that he has failed his A sample. The drug was amphetamines," British Wrestling's chief executive Colin Nicholson said.
Dykun won gold in the 2010 Commonwealth Games in the 66kg category and is seen as one of Britain's best hopes of a medal at this summer's Olympics.
He will now miss the Games if his B-test returns positive, and has already been banned from competing and had his funding stopped.
"He is immediately suspended from competition and funding," Nicholson added.
"Under no circumstances do we condone drug-taking in any form - whether it be recreational or performance-enhancing.
"British Wrestling will not tolerate such behaviour from anyone
"This is evidence that we are determined to work in partnership to root out anyone mis-using substances."
Dykun missed recent Olympic qualifying events in Bulgaria and China and is now barred from competing at another qualifier in Helsinki this week.
He moved to Great Britain in 2003 as part of British Wrestling's controversial initiative to get eastern European athletes to help home-grown wrestlers develop into medal prospects - Britain's last Olympic medal in the sport came in 1984 when Londoner Noel Loban won bronze.
British Wrestling insisted that the athletes would only be sparring partners, but the organisation performed a U-turn and permitted the wrestlers to compete for Britain.
The move caused outrage amongst British wrestlers who were determined to compete at London 2012, and the foreign imports, some of whom do not have passports, have been labelled 'Plastic Brits'.
British Wrestling will decide the make-up of their team for the Olympics on May 10.