That would appear to end any prospect of Neymar playing again this season, with the Ligue 1 season due to end on June 3 and the Champions League final, if PSG were to get there, a week later in Istanbul.
PSG, still waiting for a maiden Champions League title, will bid to overturn a 1-0 first-leg deficit in the last 16 against Bayern Munich in Germany on Wednesday.
Neymar, who has scored 18 goals in all competitions for his club this season, was in fine form for the French champions before the World Cup break.
But the 31-year-old has netted only three times in nine appearances since returning from Qatar, where he injured the same ankle playing for Brazil.
He came off with a sprain in his country's 2-0 win over Serbia in their opening game and didn't play again in the group stage.
The ex-Barcelona man returned in the knockout rounds but Brazil lost to Croatia on penalties in the quarter-finals, despite Neymar putting them ahead in extra time in that game.
Neymar's fitness has regularly been a concern for PSG, ever since he signed from Barcelona for a world-record fee of 222 million euros ($264m) in 2017.
In his first season at PSG, a fractured metatarsal ruled him out of the second leg of their Champions League last-16 tie against Real Madrid, which they lost.
He didn't play again for his club that season and faced a race against time to be fit to play for Brazil at that year's World Cup in Russia.
The following year another metatarsal injury saw him miss the last-16 tie against Manchester United as they again went out in the first knockout round.
Neymar has scored 118 goals in 173 games for PSG, but has missed more than 100 games due either to injury or suspension.
PSG are also without Presnel Kimpembe against Bayern on Wednesday, with the France centre-back set to miss the rest of the season due to an achilles injury.