Chelsea forward Mykhailo Mudryk said he is shocked after being contacted by the Football Association over an adverse analytical finding following a routine anti-doping test.
The 23-year-old Ukraine international, and the London club, confirmed that a urine sample had produced the adverse finding.
"Both the Club and Mykhailo fully support The FA's testing programme and all our players, including Mykhailo, are regularly tested," the statement said.
"Mykhailo has confirmed categorically that he has never knowingly used any banned substances. Both Mykhailo and the Club will now work with the relevant authorities to establish what has caused the adverse finding."
Mudryk, who joined Chelsea in January 2023 for an initial fee of £62 million, has struggled for first-team opportunities this season and has largely been used as a substitute in the Premier League.
He played no part in the club's last five games with manager Enzo Maresca saying that was down to illness.
In a statement on Tuesday, Mudryk, who is provisionally suspended, pleaded his innocence.
I stand with you, Mykhailo Mudryk 💙 pic.twitter.com/5ICYUiqd59
— 𝙒𝙝𝙞𝙯𝙯 (@CFC_Whizz) December 17, 2024
"I can confirm that I have been notified that a sample I provided to The FA contained a banned substance," Mudryk said on his Instagram page.
"This has come as a complete shock as I have never knowingly used any banned substances or broken any rules, and am working closely with my team to investigate how this could have happened.
"I know that I have not done anything wrong and remain hopeful that I will be back on the pitch soon. I cannot say any more now due to the confidentiality of the process, but I will as soon as I can."
World governing body Fifa's guidelines say the maximum ban for an anti-doping violation is four years.
The FA were yet to comment on the matter.