Videos posted online depict a gathering of numerous men, predominantly clad in black attire with balaclavas obscuring their faces, as they wander through the streets.
Police say during the attack three Lille fans were hurt in total, all three of whom were treated and then discharged from Bologna's Sant'Orsola hospital.
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Lille are in contention for a spot in the play-offs for the Champions League's last 16 as they sit 17th, while Bologna have a single point after four matches and are fighting to not be eliminated.
(Except for the headline, this story has not been edited by staff and is published from a syndicated feed.)