British sprinter CJ Ujah said he was "shocked and devastated" after a positive drugs test that could see Team Great Britain stripped of their Olympic silver medal in the 4x100 metre relay.
The 27-year-old ran the first leg of the final in Tokyo as Britain narrowly missed gold, but has been provisionally suspended after prohibited substances showed up in tests.
"To be absolutely clear, I am not a cheat," Ujah said in a statement to the PA news agency on Saturday.
"I have never and would never knowingly take a banned substance."
On Thursday Ujah was informed of an Adverse Analytical Finding (AAF) from a test carried out during the Olympics, showing the presence/use of muscle-building ostarine and S-23.
Ujah's relay teammates were Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake, whose medals will also be at risk if the positive is confirmed.
In his statement, Ujah said: "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 teammate.
"I am respecting the formal processes and will not be making any further comment until it is appropriate to do so."