Neymar limped off after just eight minutes of Brazil's 1-0 friendly win against Cameroon on Wednesday, AFP reported.
The Brazilian forward had treatment for an apparent groin problem after just five minutes and collapsed to the turf soon afterward to boos from the crowd in the central English town of Milton Keynes.
In Paris, Mbappe hurt his shoulder in a nasty fall as World Cup winner France ended its year on a high note with a 1-0 win over Uruguay at the Stade de France.
But the victory was overshadowed when Mbappe was hurt after falling awkwardly as he challenged the diving Uruguay goalkeeper Martin Campana for the ball.
France coach Didier Deschamps said the news on Mbappe, the 19-year-old forward who shot to global prominence at the World Cup, was "not necessarily reassuring, but not worrying either.
"He had some shoulder pain after his fall and he has to have tests tomorrow morning, but there is no serious concern," Deschamps said.
Neymar played down his injury, saying in an Instagram message that "it was nothing serious".
Brazil team doctor Rodrigo Lasmar also said it did not appear to be a serious problem.
"He felt discomfort," Lasmar said. "He will need a bit more time to evaluate it and take a scan, but in principle it is not a serious injury."
PSG coach Thomas Tuchel will be hoping that both of his star players are fit to play when the French champion hosts Liverpool in Paris on Wednesday with both sides chasing qualification for the knockout phase of the Champions League.
PSG sits third in Group C, one point behind Liverpool which is equal on points with first-placed Napoli.
Neymar's replacement in the Brazilian lineup, Everton's Richarlison, headed in on the stroke of half-time to secure victory for the Selecao.
France won thanks to Olivier Giroud's 52nd-minute penalty.
PSG faces Toulouse in Ligue 1 on Saturday when Liverpool plays Watford.