WATCH Ligue 1 LIVE on beIN SPORTS | via Foxtel, Kayo, Fetch & beIN SPORTS CONNECT
Mbappe is expected to miss PSG's UEFA Champions League Round of 16 first leg against Bayern Munich on 15 February (AEDT) after suffering a hamstring injury in the win at Montpellier on Thursday (AEDT).
Facing three weeks on the sidelines, Mbappe should also sit out Ligue 1 games against Toulouse, Monaco and Lille, as well as the Coupe de France clash with Marseille.
Considering Mbappe has 25 goals in 26 appearances for PSG this season, it is a major blow at a significant stage of the campaign, with Neymar also on the injured list.
The Toulouse game comes on Sunday (AEDT) as PSG looks to extend its five-point lead over second-placed Marseille, with Lionel Messi heading into the fixture without his fellow star attackers.
Galtier has considered whether he has played Mbappe too much since the France striker returned from Qatar 2022. His verdict is that PSG has protected Mbappe as much as possible.
"We are in a unique season, with a [FIFA] World Cup in the middle," Galtier said, "and I realise that at many other clubs with many internationals, there has been fatigue that has generated automatically and injuries.
"As a philosophy, I am in the habit of saying injuries are part of the job.
"We're sorry above all for Kylian. He is a competitor and always wants to be involved, but we can't have a season where we don't have physical problems, that's part of a season and part of the competition.
"It's even more so for a club with internationals who are in demand all the time, as much with club as with country."
Galtier said PSG "took a lot of precautions for Kylian's return".
The striker reported for duty with the capital giant in the midweek after France's FIFA World Cup final penalty shootout loss to Argentina in December, illustrating his eagerness to get back into club action.
He was then allowed a holiday in January, with Mbappe travelling to the United States for that break.
"I don't think Kylian played too much," Galtier said, "and from the moment you play, there is always an element of risk."
Veteran defender Sergio Ramos, hit by a thigh problem at Montpellier, is another who will sit out the Toulouse game. The onus will fall on Messi to drive PSG to victory, and the Argentine great scored in the 3-1 success at Montpellier.
"Leo Messi was able to take matters into his own hands against Montpellier, as soon as Kylian Mbappe and Sergio Ramos went off," Galtier said.
"He was a natural leader and the players put themselves at his service. I congratulated everyone for doing the work necessary to get this victory, which was difficult to obtain.
"The absence of Neymar and Kylian Mbappe is inevitably damaging since there were many connections between these three players. I now have to organise the team, taking into account these combined absences.
"Leo Messi will continue in his usual role. It will be up to the players who will be at his side to seize the opportunities and for everyone to raise their level of play."