The child, named Kenzo, is suffering from brain cancer and was invited along to see his beloved Marseille in action in their last game of the season against Ajaccio.
Kenzo was there along with a children's charity and was given hospitality in a special box at the Stade Francois Coty for Saturday's game.
His mother, Amandine, has told RTL that Ajaccio fans forced their way in and attacked the youngster. His father was also allegedly punched multiple times before club security arrived to intervene.
Kenzo had his shirt ripped off and the attackers set it on fire, according to Amandine, and then spat in the food that was served.
"My son was taken care of urgently, he was shocked," she said. "He was struggling to get over it, his eyes were all red and his face was swollen, he was crying and he was shaking and he couldn't breathe."
Ajaccio have released a statement condemning the "unspeakable" acts of their supporters.
"[Kenzo] had expressed his dream of meeting the players of Olympique de Marseille, the club of his city and his heart," the statement read.
"Kenzo and his family were invited to the François-Coty stadium on the initiative of the Rotary Club and the president of Air Corsica, so that the child realizes his dream during the [Ajaccio vs Marseille] meeting this evening.
"The dream quickly turned into a nightmare when Kenzo and his parents, who came in the colors of Olympique de Marseille, were shamefully abused by individuals who broke into their dressing room.
"Alerted, the security of the club intervened. Kenzo and his family were taken care of by the club's services and accompanied to the changing room area so that the child could fulfill his dream.
"These individuals in no way represent the values
"Even the most extreme stupidity cannot excuse this behaviour! The club strongly condemns these unspeakable acts! AC Ajaccio will shed full light on these shameful actions. As soon as the individuals have been identified by our services, we will file a complaint against them. AC Ajaccio is in solidarity with little Kenzo and his parents."