Two Celtic fans have been hospitalised with stab wounds after violence before the Scottish champions' UEFA Europa League match in Roma against Lazio.
Italian police say the stabbings occurred in downtown Rome after a brawl outside a pub.
Police also say two Celtic fans were stopped for resisting police and a third fan was stopped for obscene acts.
Also, five Lazio fans were stopped for possession of dangerous materials such as baseball bats and knives at an event featuring fans of both clubs.
Some 9,000 Celtic fans were slated to attend the match at the Stadio Olimpico.
One end of Lazio's stadium will be closed for the match as punishment by UEFA for racist incidents at a previous game against Rennes.
UEFA also opened disciplinary cases against Celtic and Lazio after fans traded anti-fascist and fascist gestures during Celtic's 2-1 win in Glasgow last month.
Meanwhile, Ukrainian police say they have detained 12 people involved in a brawl between about 100 soccer fans in Lviv.
The incident happened late on Thursday, a day before French club Saint-Etienne was to play Olexandriya in the Europa League.
Police say Ukrainian, French and German fans were involved in the fight. It was stopped after various police units were rushed to the scene.
Police detained four Lviv locals, said to be between the ages of 20 and 22, and eight foreigners.
Two police officers were injured.