Two Liverpool fans have been injured overnight in clashes ahead of Thursday's Europa League game with Napoli, police sources said.
Media reports added that a third Liverpool fan was in hospital in a non-serious condition following a separate incident where a gang of youths armed with knifes approached the English supporters.
English tourists mistaken for Liverpool fans were also accosted by locals at a restaurant with reports saying stones were thrown.
Italian police will be on high alert at Napoli's San Paolo stadium later. Youths damaged the goals and the pitch when breaking into the ground over the weekend.