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.
The victim, a 53-year-old man said to be a Liverpool fan, suffered a head injury and was taken to a local hospital in a critical condition.
UEFA slammed the attack as "vile", but will wait until "full reports" have been received before deciding to take any action themselves.
"UEFA is deeply shocked by the vile attack that occurred ahead of the Liverpool FC v AS Roma match and our thoughts are with the victim and his family," a statement from the governing body read.
"The perpetrators of this ignominious attack have no place in and around football and we trust they will be dealt with utmost severity by the authorities.
"UEFA is waiting to receive full reports before deciding on potential disciplinary charges."
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