Thomas Tuchel is awaiting the results of a scan on Monday after Neymar was carried off on a stretcher at the end of Paris Saint-Germain's loss to Lyon.
Neymar appeared to suffer a serious injury, amid reports of a broken ankle, following a challenge from Thiago Mendes late in Sunday's surprise 1-0 Ligue 1 defeat at home to Lyon.
PSG star Neymar was in tears as he left the field on a stretcher in stoppage time, with Mendes sent off after a VAR review in the French capital.
Asked about Neymar post-game, PSG head coach Tuchel told Telefoot: "No news, he's with the doctors and we have to wait for the exams tomorrow."
Neymar's injury compounded PSG's woes as the French champions slumped to their fourth Ligue 1 defeat of the season and a first home loss to rivals Lyon in the league since 2007 – the visitors snapping a 12-match winless streak.
Tino Kadewere scored the only goal at Parc des Princes, putting Lyon ahead after Karl Toko Ekambi pounced on Presnel Kimpembe's error.
PSG have now lost four of their first 14 Ligue 1 games this season, their worst tally of defeats at this stage since 2009-10, when the club finished 13th.
The result left PSG third in the standings, a point behind leaders Lille and Lyon through 14 games as pressure mounts on Tuchel.
"It's very clear we weren't ready to play a competitive match. We made easy mistakes in dangerous situations," said Tuchel, whose side mustered just seven attempts.
"We didn't play in a disciplined way, we didn't follow the plan. We saw a very mentally tired team after Manchester United, Montpellier and [Istanbul] Basaksehir. It's not a good game in general, I saw a game with a very low level."
Tuchel added: "It doesn't change anything, you can never control the result but this performance is not enough. It's our fault. If we give gifts like that, it means that it's not serious enough because we have the qualities to win every match.
"We're going to push again. We made some steps forward, but today is a big step back."
