Neymar limped off in the 12th minute on Sunday as Brazil drew 1-1 against Nigeria in a friendly in Singapore.
PSG said that an MRI scan showed that their star player had suffered “a grade two lesion” in his left hamstring.
If he is out until November 11, Neymar will miss four French league matches, including a trip to Marseille on October 27, and home and away Champions League games against Bruges.
The world’s most expensive player had been due to make his champions League return against Bruges next Tuesday after serving a two-match suspension.
This latest in a catalogue of injuries since joining PSG in 2017 came after a promising start to the season with four goals in five Ligue 1 matches.
