Lille say two fans have been stabbed in a “cowardly and intolerable attack” before their Champions League match against Bologna on Wednesday.
The Ligue 1 club warned fans to “exercise vigilance” after learning of the incident.
Around 80 people, believed to be Bologna supporters, assaulted around 30 Lille fans outside a bar in the city’s university district while armed with metal bars and belts, according to Italian media, which cited local police.
Three Lille fans in total were hurt, and treated in hospital before being discharged, police said.
Lille said in a statement: “The club unreservedly condemns this cowardly and intolerable attack, which contravenes all the values of football and popular support.
“We offer our support to the supporters who are victims of these attacks and wish them a speedy recovery.”
Lille are in contention for a Champions League last-16 play-off spot – they are 17th in the 36-team table on seven points – while Bologna have a single point after four matches and are fighting against elimination.
