There are reports of serious crowd trouble outside the Coppa Italia Final venue with up to four men shot.
The match kicks off at the Stadio Olimpico at 20.00 UK time (19.00 GMT) in Rome.
Fans have been flooding into the city all day, as 30,000 are expected to make the journey from Florence and as many coming up from Naples.
However, there are reports of serious crowd trouble in the Tor di Quinto area of the city, where Napoli fans allegedly tried to break through a security cordon.
According to the Corriere della Sera, hooligans attacked the police under a viaduct and gunfire was heard.
There are claims a 31-year-old man received two gunshot wounds to his arms, but his life is not thought to be at risk.
He was taken to hospital and is likely to undergo surgery, but his condition is not thought to be serious.
News agency Ansa maintains there were four men injured - two Napoli fans shot (one hit in the torso) and another a 43-year-old police officer struck in the hand.
La Gazzetta dello Sport claim it was an ambush by Roma ultras on a group of Napoli supporters, including a plain clothes police officer.
In that case, it could well have little to do with the game and instead be a targeted attack on that particular group.
TG1 report the gun was fired by a shopkeeper who was frightened by the ultras, while there are also suggestions the fourth man injured was simply a passer-by who got accidentally caught up in the fighting.
There are suggestions from La Repubblica that it might've been a nailbomb rather than gunfire which sent metal fragments spraying into the air.
In a separate incident near Rieti, a group of Fiorentina fans on their way to the game attacked some Napoli supporters at a motorway service station, but three men were treated for minor injuries.
There is also chaos in the city, as reports of huge traffic jams with buses of Fiorentina supporters blocked on the motorway for hours.