Jamaican sprinter Nesta Carter has been named in reports as one of the athletes who retrospectively failed a drug test at the Beijing Olympics in 2008.
The Jamaica Gleaner newspaper reported the 30-year-old, a two-time Olympic gold medallist in the 4x100 metres relay, returned a positive test for the banned stimulant methylhexanamine when his 'A' sample was retested.
The news, if confirmed, could have major implications for Usain Bolt, who, as a team-mate for Carter, could be in danger of losing his relay gold from Beijing.
The International Olympic Committee retested 454 samples from the Beijing Games, with 31 testing positive.
Carter also won relay gold at the 2011, 2013 and 2015 World Championships, all alongside Bolt.
Carter's personal best over 100m of 9.78 seconds ranks him as the sixth fastest man in history and he also won bronze in the individual event at the 2013 World Championships.
Any possible sanction will depend on the result of the re-testing of his 'B' sample, which is awaited.
The World Anti-Doping Agency website lists methylhexanamine as a specified stimulant which is banned in competition.
WADA say it has been considered a stimulant since 2004 and was reclassified in 2011 to become a 'specified substance'.
It defines a specified substance as one which is more likely to be 'susceptible to a credible non-doping explanation' and therefore can come with a reduced sanction.
News about Carter, if confirmed, would deal a further blow to the credibility of athletics, which is still looking to recover from the revelations about state-sanctioned doping in Russia, which has seen the country's athletes banned from international competition.
A decision about their participation at the Rio Olympics in August will be made by the sport's world governing body the IAAF on June 17.
The reputation of the men's 100m, the sport's blue-riband event, has also come under threat, with two-time drug cheat Justin Gatlin posing a serious, if so far unsuccessful, challenge to the domination of Bolt, dubbed the 'saviour' of athletics.
The re-testing of samples from the 2008 and 2012 Olympics were targeted at athletes who could potentially participate in Rio.
The re-tests from London 2012 revealed 23 positives out of 265 samples.
The IOC have already confirmed the re-analysis programme from the two Games is to be extended, meaning the potential for more failed tests.
Carter's agent, the Jamaican Olympic Association and the IOC have been asked for comment.