Neymar is expected to be out for four weeks after the Paris Saint-Germain star suffered a hamstring injury on international duty.
The Ligue 1 club confirmed in a club statement on Monday that the Brazilian has undergone an MRI scan, which confirmed a grade 2 lesion of the left ischiosis-tibial femoral biceps, a muscle in the thigh.
An assessment will be carried out in eight days' time, but he is expected to miss around a month of action.
Neymar was forced off after just 12 minutes of Brazil's 1-1 friendly draw with Nigeria in Singapore, and replaced by Bayern Munich's Phillipe Coutinho.
He had only recently returned to action for his club side after being left short of match fitness due to his summer transfer saga with Barcelona.
Nevertheless, he still managed to score four goals in five Ligue 1 outings, including the winners in three 1-0 wins. PSG went into the international break top of the French table, two points clear of second-placed Nantes with nine games played.
There was some good news for PSG fans, with several other first-team players closer to returning to full fitness.
Julian Draxler and Colin Dagba are set to return to full training with the rest of the squad this week, while Neymar's strike partners Edinson Cavani and Kylian Mbappe are moving along in their rehabilitation from hip and hamstring injuries respectively.
As well as Neymar, PSG boss Thomas Tuchel has been reliant on players such as former Stoke forward Eric Maxim Choupo-Moting and summer signings Pablo Sarabia and Mauro Icardi in attack.
Neymar's return to match-winning form has bailed PSG out more than once since his return, though he couldn't prevent a shock 2-0 defeat at home to Reims.
Following the international break, they face two away fixtures in the league and in Europe. Nice await in Ligue 1 before PSG will look to continue their 100 per cent record in the Champions League group stage against Club Brugge, before returning home to face Marseille in a glamour tie to round off October.
If the four-week projection is correct, Tuchel may be without Neymar until after the next international break in mid-November.