Usain Bolt could lose one of the three golds he won at the 2008 Beijing Olympics.
Reuters report that the 'A' sample of one of his team-mates in the 4x100m, Nesta Carter, was found to contain the banned substance Methylhexanamine.
The news comes after the retesting of 454 samples from the 2008 Games.
Carter, who along with his agent has not replied to requests for comment, will face sanctions if his 'B' sample also tests positive for the substance.
The 30-year-old ran the first leg for Jamaica's 4x100m relay team in Beijing, which also included Michael Frater, Asafa Powell and Bolt.
The team took gold in what was then a new world record of 37.10 seconds, ahead of Trinidad and Tobago and Japan.