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 forward Mykhailo Mudryk has been suspended.
Mydryk was suspended after he failed a doping test, the Premier League club said on Tuesday.
However, his suspension is on a provisional basis.
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.”