Amiens hospital said that 29 people were injured in the collapse.
According to reports, a barrier buckled as fans celebrated Fode Ballo-Toure's goal, and dozens fell about one and a half metres onto the pitch.
Joannin also apologised for his initial comments after the incident that seemed to blame Lille fans.
A Lille fan who was at the match said: "It was really carnage".
The Amiens prosecutor has already opened an investigation to determine the causes of the accident.
Alain Gest, president of Amiens Metropole, was quick to counter, claiming: "I would like to point out that what has happened has absolutely nothing to do with the Stade de la Licorne. We hope this is not too serious". "Our supporters are irreproachable and professional football demands the best organisation".
Amiens said in a statement: "Amiens and its leadership wants to express its solidarity with the injured Lille supports and their family and assure that their health is more important than anything else".