Croatia are facing possible sanction after their fans lit flares and let off smoke bombs to celebrate two first-half goals in their opening match against the Republic of Ireland.
A spokesman for European football's governing body told reporters in the Polish capital Warsaw that the organisation's Control and Disciplinary Committee would discuss the case on Friday.
An AFP reporter at the match in Poznan, western Poland, on Sunday said that at least two flares were clearly visible in one section of the crowd, as ecstatic Croatia fans marked Mario Mandzukic's third-minute header.
The stadium announcer issued an appeal to fans to behave but at least four more flares were lit while a smoke bomb was let off and curled over the pitch after Nikica Jelavic added Croatia's second in the 43rd minute.
Croatia won the Group C match 3-1.