Maybe the worst case would be him missing rest of the world cup, and not play in a few easy games at first, then 20-30 minutes in other games and then he could play 70+ minutes for PSG when they need him in the UCL, that would be the worst case, and even that's not bad. Better case would be him being ready by quarter or semi finals during world cup, and he would be fully ready when he goes back to PSG.
Most chances if he has serious trouble then surely it's going to hurt his team in next round matches, but there is nothing serious problem going to happen for the PSG because they have enough firepower in Ligue 1 which can give them good advantage and for Champions League we have more than two months which will be helpful for them for having better things.