(CNN)British sprinter Chijindu Ujah, who won a silver medal in the 4x100m relay at the Tokyo Olympics last week, has been provisionally suspended for a doping violation, the Athletics Integrity Unit (AIU) announced on Thursday.
Olympic silver medalist Chijindu Ujah provisionally suspended for doping violation
If the suspension is upheld, all four members of Great Britain's relay team -- which finished behind Italy by one hundredth of a second in Tokyo -- face being stripped of their medals. Canada would be promoted to silver and China to bronze.
According to the AIU, Ujah exhibited the "presence/use of a prohibited substance (Ostarine and S-23)" from testing conducted during the Games.
A statement said: "The AIU now awaits the conclusion of the ITA [International Testing Agency] proceedings ... 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."
Ostarine and S-23 are both classed as Selective Androgen Receptor Modulators (SARMs), according to the US Anti-Doping Agency -- a class of therapeutic compounds with anabolic properties that lead to bone and muscle growth.
The ITA said that the sample was collected during an in-competition test on August 6 after the 4x100m relay final, and added that Ujah has the right to request an analysis of his B-sample.
If the adverse finding is confirmed in the B-sample -- or if Ujah does not choose for the B-sample to be analyzed -- then the case is passed on to the Anti-Doping Division of the Court of Arbitration for Sport (CAS) for adjudication.
CNN has contacted Ujah's representatives for comment, while British Athletics said it does not comment on ongoing anti-doping processes.
Ujah ran the first leg of the Olympic 4x100m relay final for Great Britain, which led the race until Italy's Filippo Tortu pipped Nethaneel Mitchell-Blake on the line.
The ITA confirmed that if one athlete of a relay team is found to have committed a doping offense, then each member of the team is disqualified from the event; each athlete also has to forfeit any medals and prize money.
The AIU also announced on Thursday that three other athletes have been provisionally suspended for doping violations during the Tokyo Olympics.