At least one Liverpool fan has been stabbed and several others were injured in violence ahead of their team's Europa League tie in Naples.
Alexander Philips from Liverpool was set upon in the city's via dei Cimbre, local police said.
The 53-year-old football fan was knifed in the head but did not go to hospital, according to a spokesman. His two companions, aged 44 and 43, were injured.
In a separate incident, three other British Liverpool fans were attacked by a gang of Italians wielding sticks and iron bars.
Gary Brown, 50, his son Adam, 17, and a friend of his other son, Ross Hazeldene, 23, were assaulted in Piazza Garibaldi in the city centre after having drinks in a bar, Naples police said.
They had just left the bar and were heading back to their hotel when they realised they were being followed, the spokesman said.
"Realising the danger they were in, they started to run towards their hotel but the group caught up with them at the corner of Garibaldi Street and Piazza Garibaldi," he said. "At this point they were attacked with sticks and iron bars."
Mr Brown's other son, Daniel, 23, was with them but escaped injury. The men, from Bedfordshire, went to hospital briefly but have since left, the spokesman said. None of the injuries was thought to be life-threatening.
Three men were arrested and detained in custody on suspicion of causing serious injury in connection with the second incident. They were named by police as Marco Marzano, 30, a previous offender from Naples; Mirko Fiorentino, 25, from Naples; and Gerardo Lucio, 48, from nearby Avellino. A variety of weapons - including a baseball bat, three 4ft aluminium bars and a 5ft long piece of wood - were recovered from the home of one of the arrested men.
Police numbers were stepped up at the Stadio San Paolo as officers tried to keep disturbances to a minimum. Around 1,200 officers were on duty, more than one for every Liverpool fan, in an attempt to reduce the chance of further trouble.