Celtic have imposed a lifetime ban on a fan they say was responsible for displaying an offensive banner and assaulting a steward during Thursday's Europa League match against Udinese.
The club report that the individual was arrested by police in Italy.
Celtic also aim to identify those responsible for setting off flares at the Stadio Friuli.
Manager Neil Lennon has condemned a "rogue element" of fans for letting the club down with their behaviour.
"We are in possession of video and photographic evidence from the match and clearly, when those responsible are identified, the club will take the appropriate action," read a statement on the club website.
"Celtic is rightly proud of all that our supporters have achieved and the magnificent reputation they have earned across Europe over many years.
"It is extremely disappointing therefore that the otherwise excellent behaviour of the vast majority of Celtic supporters, and the reputation of the club, has been undermined in this way, by the actions of a handful of people."