The four face charges including assault and were due to appear in court in Manchester, Ceneda Flabio, an official at the Italian consulate in Manchester, said Wednesday. Flabio said he did not know the individual charges and no details were immediately available from Manchester police.
Twenty-one people were arrested Tuesday, including seven Italians. Police said that some of those detained were in possession of bladed and offensive weapons.
Before kickoff, fans from both clubs threw bottles and other objects at police lines outside the stadium and taunted each other with soccer chants.
"There was some aggression outside Old Trafford but no reports of people being hospitalized," Flabio said.
There were minor clashes as Italian fans returned to the city center after United won 7-1 - its biggest victory in the Champions League - and advanced to the semifinals 8-3 on aggregate.
There was a heavy police presence for the match because of the trouble last week during the first leg in Rome, where Italian police clashed with United fans inside the stadium.