Great Britain sprinter CJ Ujah, part of the men's 4x100m team who won silver at the Tokyo Olympics, has been provisionally suspended by the Athletics Integrity Unit for an alleged anti-doping breach.
Ujah, 27, was part of the British quartet alongside Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake who were beaten on the finish line by Italy.
The AIU announced on Thursday that following the conclusion of the Games, the doping control laboratory in Tokyo also notified the International Testing Agency of an additional 'adverse analytical finding' from testing during the Olympics.
Ujah was found to have presence/use of a prohibited substances ostarine and S-23, which are selective androgen receptor modulators (SARM) and help with building muscle.
If the case against Ujah is proven, he could face losing his relay silver medal along with the rest of the British team.
As well as the British athlete, Bahrain's 1500m runner Sadik Mikhou, Georgian shot-putter Benik Abramyan and Kenya sprinter Mark Otieno Odhiambo have also been provisionally suspended following adverse tests, the AIU confirmed.
A statement from the AIU read: "The AIU now awaits the conclusion of the ITA proceedings against the above athletes, which will determine whether any anti-doping rule violations have been committed and what consequences (if any) should be imposed in relation to the Olympic Games.
"Any consequences beyond the Olympic Games to be imposed upon the athletes under the World Athletics Anti-Doping Rules will be determined following the conclusion of the ITA proceedings."