Saracens are subject to a misconduct complaint after playing prop Titi Lamositele when he may have been ineligible in January’s Champions Cup win against Racing 92.
The tournament organisers were informed by the club that United States international Lamositele’s work permit expired the day before the match.
Saracens beat Racing 92 to reach the quarter-finals.
The win came less than 24 hours after being relegated from the Premiership.
An independent disciplinary committee will hold a hearing at 18:00 GMT on Friday.
A European Professional Club Rugby (EPCR) statement said that Lamositele may have been ineligible when he came on as a replacement in the 60th minute “due to an inadvertent administrative error on behalf of the club”.
The 24-year-old was eligible when Saracens’ matchday squad was announced, but his work permit had expired before the game on 19 January.
Three-time European champions Sarries had been relegated from the Premiership the day before the match following persistent salary cap breaches.