An Arsenal fan was stabbed in the leg and two others were injured in incidents before Wednesday's Champions League match in Rome, the Premier League club has said.
The stab victim was attacked after AS Roma fans boarded a bus taking Arsenal supporters to the Stadio Olimpico, a club spokeswoman said, adding that the victim was not in a life-threatening condition.
The others suffered head injuries in incidents outside the ground.
"Arsenal Football Club and the Metropolitan Police deplore the incident as the safety of our supporters is the highest priority," a statement said.
An Arsenal spokeswoman added: "A male Arsenal fan was believed to be stabbed outside the stadium.
"Roma fans threw stones at a bus, smashing windows, and an individual allegedly entered the bus and stabbed a fan."
A Foreign Office spokesman said: "We are aware of the incident that happened in Italy and we are providing consular assistance."
Violence has marred several Roma matches in Europe in recent years, most prominently in two games against English club Manchester United in 2007.
The incident will call into question Rome's ability to host this season's Champions League final.
Arsenal reached the quarter-finals of the competition with a 7-6 penalty shoot-out win on Wednesday after a 1-0 defeat on the night left the score level on aggregate.Reuse content