Legia Warsaw have confirmed that they are currently under investigation after fielding an ineligible player against Celtic on Thursday evening.
The Champions League third qualifying-round tie saw Celtic beaten 2-0, which eliminated the Scottish champions from the competition.
"UEFA has opened an investigation on the participation by Bartosz Bereszynski," read a Legia statement.
Bartosz Bereszynski came on as a substitute during the final stages of the match on Thursday evening despite being suspended for the fixture.
Bereszynski had been sent off in Legia's final Europa League match against Apollon Limassol.
