Greater Manchester Police arrested five men after a scuffle broke out between Liverpool and Manchester United supporters at Old Trafford following Thursday night's Europa League last-16 tie.
Liverpool progressed into the quarter-finals with a 1-1 draw, which took Jurgen Klopp's side to a 3-1 win on aggregate.
Towards the end of the game, some punches were thrown between fans when a group of visiting supporters unfurled a Liverpool flag on the top tier of the East Stand.
According to the Liverpool Echo, two Liverpool fans were arrested on suspicion of affray, while another was detained by police on suspicion of causing criminal damage after a minibus window was smashed.
A fourth Liverpool fan was cautioned after getting arrested for letting off a flare and a United supporter was taken in by police for allegedly being drunk and disorderly.