Olympic silver medallist CJ Ujah denies wrongdoing and says he is “shocked and devastated” after a positive drugs test.
Ujah, 27, ran the first leg as Great Britain’s 4x100m men’s relay team narrowly missed out on gold in Tokyo.
He has been provisionally suspended after a test showed the “presence/use” of two prohibited substances.
“To be absolutely clear, I am not a cheat,” said Ujah in a statement to the PA news agency on Saturday.
“I have never and would never knowingly take a banned substance.”
Ujah was informed on Thursday of an “adverse analytical finding” – the presence/use of prohibited substances ostarine and S-23, which are selective androgen receptor modulators and help with building muscle.
If the case against him is proved, the British relay quartet – also including Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake – are likely to be stripped of their silver medals.
In his statement, Ujah said: “It’s taken me a few days to process the information I received on Thursday, shortly before it was made public.
“I am completely shocked and devastated by this news.
“I love my sport and I know my responsibilities both as an athlete and as a team-mate.
“I am respecting the formal processes and will not be making any further comment until it is appropriate to do so.”
The British sprinters lost out by just one hundredth of a second as they were beaten by the Italian team.
Ujah can request analysis of his B sample. Should that confirm the adverse analytical finding, the case will be referred to the Anti-Doping Division of the Court of Arbitration for Sport.
