UEFA is "deeply shocked" by the "vile attack" which left a Liverpool fan in a critical condition before Tuesday's Champions League match with Roma.
Reports emerged of violence between the two sets of fans shortly before kick-off at Anfield, as Liverpool went on to win the semi-final first leg 5-2.
Merseyside Police confirmed the force was investigating a "serious assault" of a man outside The Albert pub, located close to Anfield on Walton Breck Road.
After making a social media appeal for information, Merseyside Police confirmed the arrests of two men from Rome, aged 25 and 26, in connection with the incident.