The Brazil star limped out of PSG's 2-0 Coupe de France win over Strasbourg having appeared to twist his foot after a robust challenge from midfielder Moataz Zemzemi.
PSG manager Thomas Tuchel later admitted he was concerned for the player, who was sent to hospital for tests.
PSG has since issued a statement to confirm Neymar has hurt the same metatarsal that he broke last February in a Ligue 1 win over Marseille.
The French champion has not stated whether the €222million forward has suffered another fracture, however.
"Initial examinations have revealed a painful recurrence of his injury to the fifth metatarsal of his right foot," the statement said.
"The treatment of this injury will depend on how it evolves over the next few days. All options can be envisaged at this time."
The news is a major blow to Tuchel, whose side faces Rennes, Lyon and Bordeaux in Ligue 1 before a trip to Manchester United on 12 February for the first leg of the UEFA Champions League last-16 tie.
PSG's victory over Strasbourg came courtesy of goals from Edinson Cavani and Angel Di Maria.