Italian police have said gangs of Napoli's hardcore Ultra fans went out hunting Liverpool supporters to attack in the city last night.
There were a number of incidents ahead of the club's Europa League match at the Stadio San Paolo tonight, which resulted in five English people - two of whom were stabbed - and one Italian being taken to hospital.
Their injuries were not deemed to be serious and all were discharged after receiving treatment but it has prompted police to step up security ahead of the game.
There were three arrests made after the attacks last night and police recovered an array of weapons and Ultra paraphernalia from the home of one.
Among the weapons seized were a baseball bat, several five-foot long aluminium bars with numerous strategically-placed screws protruding and a six-foot wooden plank.
"Ultras went out seeking English fans, absolutely," said Filippo Bonfiglio, head of DIGOS, the local department which deals with terrorism and political activity.
"There are groups of violent supporters here in Naples so we could hypothesise something like this would happen but it was impossible to prevent every attack everywhere."
Trouble started at around midnight when Ultras began throwing things at English fans in a pizzeria.
The Italian owner went out to remonstrate and that was when he was injured.
Two Liverpool fans were injured after being attacked by a group of Napoli supporters before the most serious attack took place around 4am near the central Piazza Garibaldi.
A group of four fans were walking back to their hotel when they were followed and beaten up by a gang of 20-30 men.
Police said Gary Brown, 50, from Hertfordshire, and his son Adam, 17, received a knife injury and bruising respectively.
Brown's 23-year-old son Daniel was not injured but family friend Ross Hazeldene, also 23, sustained a knife wound.
All three of the arrested men have criminal records and one has been convicted of football-related violence and is banned from Napoli's Stadio San Paolo.
There will be around 1,200 police on duty for tonight's match.
"We are organising more patrols to prevent these kind of attacks," added Bonfiglio.
"But the city is so great - 1.5million inhabitants - that it is impossible to prevent and control everything."