Two Celtic fans needed hospital treatment after they were stabbed by masked attackers in Rome.
The incident happened outside the Flann O’Brien pub in the Italian capital on Wednesday night.
Celtic are due to play Lazio in a Europa League clash at the Stadio Olimpico on Thursday evening.
Italian police said the injured pair were taken to hospital for treatment.
Dennis Connelly, a fan from Kilmarnock, said: “We were just in the pub maybe the back of 11 last night and then maybe 15 or 20 Lazio fans, well I’m assuming Lazio fans, turned up with their masks on.
“They pen-knifed a guy, they stabbed a guy in the leg, now this man’s 53 or 55 years old, I’m led to believe, so that shows how cowardly they are, they’re targeting, without being disrespectful, they’re targeting the older generation.
“The staff were brilliant, they pulled the shutters down, the police appeared within about five, six, seven minutes, and that was it.”
Italian police said five Lazio fans and two Celtic supporters were arrested during the evening though it was not clear if they were all involved in the same incident.
One of the injured men remains in hospital while the other has been discharged.
Celtic had issued safety advice to fans amid tensions after a match between the clubs in Glasgow last month.
Supporters are advised to avoid wearing club colours while walking around Rome, particularly in the evening, stay in large groups where possible and keep a low profile.
A Celtic spokesman said: “We can confirm that two fans have been injured after being stabbed last night.
“Both are now in hospital and will receive every support from the club and the British consulate in Rome.
“Again we would strongly advise supporters to closely follow all guidance issued by the club.”
The Glasgow club and Lazio were charged by Uefa over “illicit chants” heard during their Europa League match on October 24.
Celtic were also charged over the display of an “illicit banner” during the game, which they won 2-1.