Chelsea forward Mykhailo Mudryk has failed a doping test, the Premier League club said on Tuesday, as reports stated the Ukraine international has been provisionally suspended.
The Blues said they were notified by the Football Association of an "adverse finding" in a urine sample provided by the 23-year-old winger.
"Chelsea Football Club can confirm that the Football Association recently contacted our player, Mykhailo Mudryk, concerning an adverse finding in a routine urine test," a club statement said.
"Both the club and Mykhailo fully support the FA's testing programme and all our players, including Mykhailo, are regularly tested.
"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 issued a statement via his Instagram account.
"I can confirm that I have been notified that a sample I provided to the FA contained a banned substance," it said.
"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."
Athletes are warned on the UK Anti-Doping (UKAD) website that they face a ban of four years if it is found a banned substance was taken intentionally.
If the violation involved a specified substance or a contaminated product, and the athlete can demonstrate they had no significant fault, ineligibility may range from two years to a reprimand, depending on the level of fault.
Mudryk has made 15 appearances for Chelsea this season and last played in a 2-0 win at German side Heidenheim in the Conference League on November 28, in which he scored his third goal of the season.
He has not featured in the past five matches in all competitions.
Mudryk joined Chelsea for a reported £88.5 million ($112 million) from Ukrainian club Shakhtar Donetsk in January 2023.
Enzo Maresca's side are second in the Premier League and top the Conference League table.