Supporters from France and Belgium were involved in a knife fight at the Lyon fan zone on Wednesday night, marking the first serious incident inside a fan zone during the Euro 2016 tournament.
The French fan was stabbed in the thigh, while the Belgian was stabbed in the buttock, reported Le Parisien, suggesting that there were at least two knives used during the attack.
Both stabbing victims were taken to hospital, although their injuries are said to be minor.
The clash raises questions as to how the supporters were able to bring weapons into the fan zone, despite the police security gates at the entrance.
The aggression kicked off before France scored two goals late in the match, apparently when France supporters were singing the Marseillaise, reported the Europe 1 channel.
"This is the first hit that we've had at a fan zone," a police source told the channel, adding that the fact supporters had managed to get knives inside was "worrying".
Police were called to the scene, but made no arrests, and the identity of the attackers for the moment remains unknown.
Officers however did arrest one person at the fan zone for letting off a smoke bomb.
A total of around 16,000 fans were at the Lyon fan zone on Wednesday, despite the rain.