Four fans were jailed after violent clashes in Rome
Manchester United fans travelling to Rome on Tuesday have been warned they will be risking their safety if they do not cooperate with Italian police.
Recent matches between United and AS Roma have been marred by violence between rival supporters.
Italian authorities have taken several precautions to avoid a repeat, such as free transport to the stadium and a voucher system for ticket collection.
Greater Manchester Police have urged fans to be on their best behaviour.
The two clubs are meeting in the Champions League quarter final on Tuesday.
The free transport has been organised for United fans in a bid to avoid trouble previously seen on the Duca d'Aosta bridge.
Greater Manchester Police said anyone choosing to make their own way to the stadium - or those planning to buy tickets from touts - could be putting themselves in danger.
In a statement, the force said that their Italian counterparts "have a robust approach to people arriving with forged tickets and general disorder".
Supt John Graves, match commander for the fixture, urged fans to take advantage of the free buses.
"Anyone choosing to make their own way could potentially run the risk of coming into harm's way," he said.
United fans will only be able to pick up their ticket at a designated ticket collection point 24 hours before the match, and need their passports as proof of identity.
"Anyone attempting to get into the game with a forged ticket could be liable to arrest," Mr Graves added.
"We aim to continue the good work that has already been achieved in previous operations of this kind and prevent troublemakers ruining the reputation of genuine football fans."
Officers from Manchester recently flew to the Italian capital to discuss policing and will also be monitoring British airports to target known troublemakers attempting to travel to Italy.
It is the fifth time the two clubs have met in the Champions League in less than a year.
In the 2007 quarter-final, three United fans were stabbed outside the Stadio Olimpico.
Scuffles also broke outside Old Trafford during the second leg, with 21 people arrested.
The teams also played each other in the group stage of this season's competition and four Manchester United fans were jailed in Italy for clashing with rival fans in Rome in December.