Saint Etienne were relegated to the second tier of France football after losing on penalties to Auxerre, who will take their place in Ligue 1 for the 2022/2023 season.
Both legs of the play-off ties ended 1-1 and Auxerre triumphed 5-4 in the penalty shootout to ensure Saint Etienne will play in Ligue 2 for the first time in 18 years.
Auxerre are back among the big boys after a 10-year absence.
Angry Saint Etienne fans thronged onto the pitch at full time, with some hurling flares in the direction of fleeing players and security.
Amid the chaos, police had to resort to the use of tear gas to disperse supporters.
A club statement said: "Despite an exceptional and reinforced deployment of nearly 500 agents, many supporters invaded the pitch at the final whistle of the match against Auxerre.
"Some were guilty of several degradations and acts of violence towards players, the security agents, police and the fans in the Pierre-Faurand stand
"ASSE strongly condemns these acts, gives its full support to those affected and will initiate the necessary legal proceedings."
"This failure must be accepted," owners Bernard Caiazzo and Roland Romeyer wrote on social media after the game.
"As major shareholders, we take full responsibility for this. In a while, we will announce important news regarding the future of the club and ours."
