Celtic's fine 2-1 victory over European champions AC Milan was marred by a thoughtless fan who ran onto the pitch and appeared to strike Milan goalkeeper Dida.
Whether Dida was justified in going to ground after what seemed to be a cheeky slap, all Celtic fans could now pay for what happened.
That would be a crying shame for the competition seeing as the club has been commended for its support by Uefa and Fifa in the recent past and Celtic fans are renowned for their vast and vocal support.
In 2005 Dida was struck by a flare thrown by Inter Milan fans in a Champions League tie and on that occasion Inter were thrown out of the competition and force to play their next four European games behind closed doors. They were also fined £132,000.
Should Celtic's punishment be as severe as the one handed out to Inter? Should they be made to pay for one fan's stupidity?
Do you fear what might happen after a great European performance?