Three people were reportedly arrested and up to 10 people injured during clashes between Liverpool and Napoli fans around the Europa League match.
The overnight clashes in downtown Naples involved knives and thrown rocks, according to the ANSA and Apcom news agencies on Thursday.
Five English supporters were reported injured along with four or five Italians, including a restaurant owner.
A sold-out crowd of 60,000 watched Liverpool and Napoli draw 0-0 in San Paolo Stadium, where five police officers were injured during clashes with Liverpool fans as they sought to maintain order.
One was taken to a local hospital for treatment on a cut hand and was allowed to return to his post at the stadium, ANSA news agency reported.
Diego Maradona led Napoli to the UEFA Cup title in 1989 but the southern club has struggled in recent seasons, and therefore hasn't hosted a foreign club of Liverpool's pedigree in years.
Napoli Mayor Rosa Russo Iervolino said she felt "enormous pain" for the injured English fans and appealed to the entire city to "exercise our well-known hospitality."
"Let's just behave as fans and avoid a scene like the one in Genoa," Iervolino told Radio Kiss Kiss, referring to last week's abandoned Italy-Serbia European Championship qualifier, which was disrupted by violent Serbia fans.
"I'm not worried about tonight's game," Iervolino added. "There will be enough police and the English police will also help out greatly by taking care of the Liverpool supporters."
This season Napoli was fined ?8,000 ($11,000) for fan trouble at its Europa League match with Steau Bucharest.
