The 23-year-old has not been seen in a Blues shirt since November 28, when he scored and completed the 90 minutes in a 2-0 victory over Heidenheim in the Conference League.
Mudryk's absence has since been attributed to illness, the Ukraine international not featuring in squads between December 4 and December 15.
According to a report by Zorya Londonsk, the £89m man has instead been made unavailable courtesy of being notified of a failed drugs test.
When did Mudryk's failed drugs test occur?
The report alleges that a banned substance was found in a test that was taken at the end of October. As it stands, only the 'A' sample' has been opened.
A 'B' sample is due to be opened across the coming days. The Football Association are yet to address the alleged situation via an official statement.
Should the 'B' sample' also be found to contain a banned substance, Mudryk faces the possibility of a suspension from football, pending an appeal.
In light of the report that emerged late on Monday night, Chelsea have since released an official statement to confirm the recent development.
It read: "Chelsea Football Club can confirm the Football Association recently contacted our player Mykhailo Mudryk concerning an adverse finding in a routine urine test.
"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.
"The club will not be commenting any further."
What is Mudryk's alleged explanation?
As per a report in the Daily Mail, Mudryk is of the opinion that a contaminated supplement is behind the failed test.
Mudryk allegedly passed a test in August, which was clear, with it claimed that he has since not changed anything in his diet since.
Furthermore, Mudryk feels that any contamination may have taken place outside of England, a result of the substance in question not being available in this country.
Written by
Darren Plant