A group alleged to have been visiting supporters of the Italian side attacked the Piebury Corner shop near the Emirates Stadium prior to the sides' clash on Tuesday night.
Piebury Corner, a 10-minute walk away from the Gunners' ground, was full of supporters when dozens of Napoli fans are alleged to have charged through, swinging belts, smashing windows, breaking chairs and chanting.
Whittington Hospital confirmed that it treated one man for a deep head wound caused by a flailing belt buckle.
As of Tuesday evening, the Metropolitan police had made no arrests, though did confirm a "football-related" incident took place at Piebury Corner and expect an update on the situation later on Wednesday morning.
Owner of the restaurant, Paul Campbell, told reporters that the attack was "completely unprovoked".
"We have had Napoli fans inside all day today, they have been having a good time and not bothering anybody at all. They have been no problem. Then we had a minority of them come in, being violent, picking up chairs and tables. There were three girls sat near me and these thugs just came in and grabbed the chairs from under the girls.
"It was completely unprovoked, I think they just picked us at random because they saw a busy restaurant and they wanted to fight someone - anyone."
A shop employee also described the damage: "I think they were Italian men with Napoli colors and scarves tied around their faces. They were shouting something in Italian, chanting and causing trouble down the street.
"There is blood all over the floor. There is a lot of damage to the shop. The tables and chairs are wrecked."