The Brazilian was pictured screaming in agony and clutching his ankle after suffering the injury in stoppage time.
It followed a poor challenge from Thiago Mendes, who was sent off.
Tino Kadewere scored the only goal of the game as PSG dropped to third in the table, one point behind leaders Lille and second-placed Lyon.
PSG boss Thomas Tuchel said Neymar would have tests to establish how serious the injury was.
“He’s with the physio and the doctors and we have to wait for the tests” he told French broadcaster Telefoot.
Neymar, 28, joined PSG for a world record fee of 222m euros from Barcelona in August 2017.
He has helped the club win three successive Ligue 1 titles as well as reach last season’s Champions League final.
As It Stood