Jerome Young, USA
World 400m champion Jerome Young failed a doping test in Paris last month, according to a French newspaper.
L'Equipe reported that the 27-year-old tested positive for the banned blood booster EPO on 23 July.
The news follows a previous test in 1999 when his blood was found to contain traces of nandrolone, though he was later exonerated of all charges.
He then won gold in the 400m relay at the 2000 Olympics - a result that could now be reversed.
Young's previous failed drug test was not revealed until last year.
After it came to light, the International Association of Athletics Federations ruled last month that the US 400m relay team should be stripped of their Sydney gold.
The International Olympic Committee executive board is scheduled to meet before the Olympics start on 13 August, and must decide whether or not the medals should be taken back.
Young will not run in Athens as he failed to make the US team.
The International Association of Athletics Federations says the American 4x400m relay team that won gold at the 2000 Olympics should lose their medals.
The team, including Michael Johnson, faces punishment after one of its members, Jerome Young, tested positive for banned substance nandrolone.
"Based on this position, we believe the medals should be taken back," said IAAF general secretary Istvan Gyulai.
The final verdict rests with the International Olympic Committee.
Young, who has protested his innocence, tested positive for nandrolone before the Olympics, but was exonerated by a USA Track and Field doping appeals board and allowed to compete in Sydney.
He did not run in the final, but was involved in the first round and semi-final.
The Court of Arbitration for Sport recently ruled that the 400m world champion should have been banned for two years, and should also lose his gold medal because of the positive dope test.
IAAF spokesman Nick Davies said the IAAF council had decided that any such ban should also have applied to relay running.
"The result of the relay will be annulled," he said. "We will now inform the IOC."
Members of the team - which also included Alvin and Calvin Harrison, Antonio Pettigrew and Angelo Taylor - have been invited to present their case, either in person or in writing, at a hearing at some future date.
The IOC executive board is scheduled to meet before the Olympics start on 13 August, and must decide whether or not the medals should be taken back.
Nigeria, Jamaica and the Bahamas were the three teams who came home behind the Americans in Sydney.
The relay medal was the fifth Olympic gold medal of Johnson's career, and he has already made clear his feelings on the matter and the possibility of losing the medal.
"The bottom line is that when Jerome Young made the Olympic team, he had been cleared to run by the USATF," he told the Dallas Morning News.
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