Ajaccio’s 1-0 win against their regional rivals on the island of Corsica was played in a tense atmosphere on Saturday.
After the game, a journalist from France 3 TV was attacked by Marseille supporters at a filling station near the stadium.
He was taken to hospital for treatment to “wounds on his face”, an AFP reporter at the scene said.
“Initial evidence points to serious acts of violence committed by a group of individuals who we are trying to identify,” Ajaccio’s chief prosecutor Nicolas Septe said.
He said the France 3 journalist was “quite seriously injured although there is no risk to his life”.
In a separate incident, a child suffering from cancer who was invited to meet the Marseille players was jostled along with his parents by Ajaccio supporters at the stadium, the Corsican club said, calling their behaviour “unspeakable”.
“The dream rapidly became a nightmare when Kenzo and his parents, who were wearing Marseille’s colours, were shamefully jostled by individuals who got into their box,” the club said.
“As soon as these individuals can be identified by our staff, we will bring prosecutions against them.”
The mayor of Ajaccio, Stephane Sbraggia, said the attacks on the journalist and the incidents surrounding the child “point to a worrying loss of values”.
It was the second incident of violence involving French football supporters in two days.
Four men were arrested in Bordeaux on Saturday after an assault on a player from their opponents Rodez led to a crucial match in the French second division promotion race being abandoned.
The match between hosts Bordeaux and Rodez on Friday was halted midway through the first half when a home fan approached the pitch and pushed over Rodez player Lucas Buades, who had just scored for the visiting team.
The match was halted and did not restart.
The source said the alleged aggressor was one of those taken into custody.
He was described as a 45-year-old man and a resident of the city of Annecy by local Bordeaux newspaper Sud Ouest.
Police allege that he invaded the pitch and “violently pushed” Buades, who was left concussed according to the referee.
The French league (LFP) will meet on Monday to discuss the incident which overshadowed the final night of the Ligue 2 season.