UEFA has opened disciplinary proceedings against Sturm Graz after an assistant referee suffered a cut to the head in their Europa League tie against AEK Larnaca on Thursday.
Fredrik Klyver appeared to be struck by a cup thrown by a spectator during the contest at Merkur Arena in Austria, leading to a long delay as he received treatment.
The players were taken off the pitch by referee Mohammed Al-Hakim as a result and, when they emerged, Klyver had been replaced by the fourth official.
A Sturm Graz statement after the match spoke of the club's shock at the situation, insisting they were "sorry that today we disappointed many football fans".
The Austrian side lost the third round of qualifying first-leg tie 2-0 and now potentially face further action from UEFA.
Europe's governing body has charged them with improper conduct of supporters and the case will be handled on August 17.
