A gang of up to 50 armed Lazio fans are believed to have set upon Spurs fans in a planned attack in Italy.
Nine Tottenham fans were injured in the attack while drinking in a pub ahead of tonight’s Europa League game between Tottenham Hotspur and Lazio in Rome.
Two people were stabbed in the onslaught - with one British man – believed to be 25 years old, in a critical condition in hospital.
The hooligans are reported to have worn motorbike helmets to disguise their identity while wielding metal bars, knives, baseball bats, belts and knuckle dusters.
Photographs show the Drunken Ship pub in Campo de Fiori was ransacked in the attack on Wednesday night shortly after 1am, with wooden bar stools thrown to the ground and blood stains visible on the street.
Italian newspaper La Repubblica claimed scenes of "urban warfare" erupted as up to 100 Ultras went on to "destroy" the venue.
One witness told the paper: "We feared the worst."
A spokesman for Rome police confirmed seven men were injured - five Britons, one Californian and one Bangladeshi.
He said a Briton, born in 1987, was severely injured and was being treated at San Camillo hospital.
"A group of about 40 or 50 people in motorcycle helmets or with their faces covered were armed and attacked the group of English football fans drinking in Campo de Fiori square," the spokesman said.
It is believed police made arrests at the scene.
A spokesman for the Foreign and Commonwealth Office confirmed it was investigating.
Spurs had released travel advice to fans on Tuesday to prevent any risk of trouble.
The statement said: “If you are making your own way to the stadium, you should travel to the south side of the stadium via the Ponte Duca D'Aosta - this is the only bridge that you should use as the home fans will use the Ponte Milvio to reach their side of the stadium.
“Italian Police will monitor both bridges closely and have a high attendance in place.
“For your safety and security and to avoid any problems, we recommend that you use the shuttle buses to reach the stadium.”
Spurs is due to release a statement about the attack later today.