Ligue 1 club Lille say two of their supporters were stabbed when a group of fans were attacked in a bar ahead of Wednesday's Champions League game at Bologna.
Lille issued a statement on social media condemning "this cowardly and intolerable attack," which they said happened on Tuesday.
"During the ambush, which is believed to have involved around eighty assailants, two of our supporters sustained stab wounds, among other injuries, and were given medical treatment," Lille said.
Lille said Italian police have reinforced the protection of its fans ahead of the game.
"However, LOSC calls on their supporters in Bologna to be extremely vigilant, to ensure that the trip takes place in safe conditions," the club said.