Mudryk is set for a lengthy spell on the sidelines, which could be as much as four years, per The Sun.
The Ukrainian, who Chelsea will end up paying around £88.5M for, failed an A-sample of a drug test in October.
Ukrainian outlet Tribuna claims Mudryk had meldonium in his system, which is a banned metabolic substance.
Meldonium has been an issue for athletes in the past, with tennis star Maria Sharapova earning a 15-month ban several years ago.
Mudryk released this statement on Tuesday: “I can confirm that I have been notified that a sample I provided to The FA contained a banned substance”.
“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”.