He can use this time to gather himself up and focus on his game at PSG again. PSG need these three important players not only healthy but also mentally strong. The Ligue 1 is pretty easy for them maybe but the Champions League doesn't forgive any weakness.
The most vulnerable is Messi, if he and his Argentina make it to the final round. if not injured, the effects of fatigue can greatly affect him to face his matches with PSG after all leagues are rolled out again. because after all, this world cup tournament will really drain the energy and mentality of the players who take part in this championship. for Neymar, I'm not sure that he has fully recovered. but he has enough rest time, before returning to play with PSG.
Mbappe, he's still young I'm sure he'll be fine after the world cup is over and come back to the club in top shape. on the other hand, the elimination of the Portugal squad over Marocco. several PSG players who defended Portugal will return to the team, such as, Vitinha, Nuno Mendes. Unfortunately, Danilo Pereira is reportedly injured. there is no certainty as to how long it will take him to recover. another formidable defender who will still be in Qatar is Hakimi.
so there are 3 PSG players who are still defending their national team in this world cup. even so, I hope that all PSG players who defend their national team will not experience problems after returning to PSG.