WATCH: Messi scores as PSG wins despite Mbappe injury
With Neymar already ruled out of the Ligue 1 match because of muscle fatigue, Mbappe was forced off in the 21st minute of PSG's 3-1 victory on Wednesday (AEDT) and clutched his hamstring as he went straight down the tunnel.
The forward's injury came after he had missed a penalty, as well as its retake for a Montpellier encroachment, though his team went on to win the game through goals from Lionel Messi, Fabian Ruiz and 16-year-old Warren Zaire-Emery.
But after Sergio Ramos also came off with injury in the first half, there was much concern after the game over some players' availabilities with less than two weeks until the first leg of PSG's Champions League last-16 tie with Bayern Munich.
Galtier eased fears over the injuries to Mbappe and Ramos, though, saying: "It doesn't seem very serious, for one as for the other.
"We will see. Obviously they are two important players. On what we saw at half-time and what we said to each other, there is not too much worry.
"Kylian took a blow behind the knee and on the muscle. Is it a contusion, a hematoma. We don't know yet. With the sequence of matches, we prefer not to take any risks.
"Sergio, when falling, hurt his adductor. We think it's not serious. He preferred to come off and not take any risks regarding the discomfort."
Despite PSG winning Ligue 1 last season, head coach Mauricio Pochettino was relieved of his duties after failing to deliver the club's first Champions League.
Galtier is bidding to avoid the same fate, though he says he expected the pressure before he came into the job.
"Yes, automatically when you sign for PSG, there is an obligation to win," he said.
"The Champions League requires you to be ready. We have players coming back, and we've just had a World Cup. I knew before coming that there was pressure."
PSG missed out on a deadline day move for Chelsea's Hakim Ziyech due to the Premier League club reportedly making an error with the necessary paperwork.
When he was asked whether he was disappointed not to have brought Ziyech in, Galtier said: "You know it. We wanted to replace the departure of Pablo Sarabia.
"Unfortunately, it didn't happen but it's the quirks of the transfer window – you have to accept it."