A Paris Saint-Germain fan injured in a fight between rival factions of hooligans from the club was in a life-threatening condition on Monday, police said.
The 38-year-old fan sustained a serious head injury ahead of Sunday's French league match between fierce rivals PSG and Marseille. Marseille went on to win the game 3-0.
The clashes involved hooligans from the two main stands at PSG's stadium Parc des Princes, the Tribune d'Auteuil and the Kop of Boulogne.
A 30-year-old man suspected of taking part in the beating was arrested just after the fight and has been held in detention.
Marseille fans had boycotted the game to protest against security measures imposed on visiting supporters.
Following several months of relative tranquility, Kop of Boulogne and Auteuil fans -- angered by their team's poor results and its owners -- started fighting again at the end of last year and clashed violently at Lille in January.
PSG are 12th in the league with just 33 points from 26 games.