Liverpool fans have been accused of planning to join forces with Lazio hooligans.
Around 5,000 supporters will make the trip to the return leg of the Reds’ Champions League semi-final with Roma on Wednesday night.
Anfield officials are already wary of the potential backlash that travelling fans will face in the Italian capital after an attack by Roma hooligans last week.
Sean Cox, a 53-year-old Liverpool fan from Ireland, remains in a critical condition as he was set upon by belt-carrying Italians before last week’s first leg.
But Andrea Cecchini, the head of the country’s state police union Italia Celere, has alleged that 1,000 fans will travel from England intent on causing trouble.
He said: “We have the certainty of the arrival of at least 1,000 English ultras.
“And considering the Lazio fans have in the past already twinned with violent fan bases from the Czech Republic, Croatia and Poland, the risk of a new alliance is very high.
“When these foreign fans arrive, there is no Fan Passport, no stadium ban or anything else.”
Roma president Jim Pallotta condemned a section of the club’s support as “f***** morons” for tarnishing its reputation through acts of violence.