TV cameras showed the Brazilian clutching at his left ankle after a heavy challenge from Lyon’s Thiago Mendes, who was sent off as a result.
Neymar’s ankle appeared to get twisted awkwardly under Mendes’ body, and he had to be stretchered off the pitch in clear distress in the dying embers of PSG’s 1-0 defeat at home to Lyon.
PSG manager Thomas Tuchel said Neymar would have tests to establish how serious the injury was.
Neymar’s injury compounded an awful evening for the reigning French champions as it suffered a surprise defeat to Lyon.
Tino Kadewere scored the only goal of the game for Lyon in the first half as PSG dropped to third in the table, one point behind leaders Lille and second-placed Lyon.
All three teams are again in action on Wednesday, with PSG at home to Lorient.
Neymar’s injury comes at the worst possible time for PSG with the draw for the last 16 of the Champions League taking place on Monday.
His hattrick against Istanbul Basaksehir last Wednesday helped PSG top its group ahead of RB Leipzig and Manchester United.
He has helped the club to three successive Ligue 1 titles as well as playing a pivotal in PSG’s run to last season’s Champions League final.