Teesside Tornado Richard Kilty could be stripped of his Olympic silver medal following teammates 'B' sample testing positive.
British sprinter CJ Ujah's B sample from the Tokyo Olympics has tested positive for banned substances, the International Testing Agency (ITA) has announced.
Ujah provided the sample on August 6, the ITA said, the same day that he was part of the British team which won silver in the men's 4x100 metres relay.
The agency said now the B sample had confirmed the result of his A sample, his case had been referred to the Court of Arbitration's Anti-Doping Division.
The court division will consider the finding of an anti-doping rule violation and the disqualification of the British relay team, the ITA said.
If the case against Ujah is proven, the British relay quartet, also including Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake, are likely to be stripped of their silver medals.
Ujah was provisionally suspended following the result of the A sample last month and released a statement on August 14 saying he was "shocked and devastated" by the outcome of the test.
He added: "To be absolutely clear, I am not a cheat and I have never and would never knowingly take a banned substance.
"I love my sport and I know my responsibilities both as an athlete and as a team-mate."
Ujah's sample returned an adverse analytical finding (AAF) for the prohibited substances ostarine and S-23, the ITA said. These substances are selective androgen receptor modulators (SARMs) and help with building muscle.
The possible forfeiture of the medals will be considered first, before the Athletics Integrity Unit (AIU) follows up to consider any sanction beyond the Games for Ujah.