Clermont goalkeeper Mory Diaw was forced off the pitch on a stretcher after one exploded next to him.
Medical staff had to attend to the 30-year-old, who lay on the deck following the incident.
Eventually, as he was stretchered off the pitch, match officials led both sets of players into the dressing rooms.
It was then announced that the match had been abandoned with the final whistle just moments away.
Montpellier were leading 4-2 in the closing minutes the firework exploded.
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After it went off, Diaw collapsed to the floor as medical staff rushed on immediately and players nearby tried to attend to the goalkeeper.
Clermont star Neto Borges received a red card after appearing to show a middle finger to the fans in the stand behind the goal.
Clermont's club doctor revealed that Diaw had been 'extremely traumatised' by the incident.
Crowd trouble has been a regularly occurring problem in Ligue 1 and Ligue 2 over the past few years.
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Almost two years ago in 2021, Dimitri Payet was struck by a missile in the crowd which forced Marseille's match against Lyon to be abandoned.
Saint-Etienne fans stormed the pitch in May 2022 and riot police had to use tear gas to disperse the crowds of hooligans, forcing players to flee.
When the match between Montpellier and Clermont Foot will be rescheduled remains to be seen.