The European and English champions are already facing relegation from the Premiership at the end of the season for breaching salary-cap regulations.
Sarries will face an independent disciplinary committee on Friday after European Professional Club Rugby (EPCR) brought a misconduct complaint against them.
Lamositele came off the bench in a 27-24 win over Racing on January 19, but may have been ineligible due to what EPCR described as "an inadvertent administrative error on behalf of the club".
