Right now both Argentina and France having fair chance for the title in World Cup with this most chances these both players will be played for some more time, and hopefully they will end this cup without any serious issue because nothing's could be tricky as full strength needed for all countries as we are entering into last 16 round and Neymar injury is surely big setback for the Brazil which is also favourite for the title.
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.
PSG is not a favorite team when it comes to the Champions League. We have seen how they have performed in the Champions League previously. Even when they have a good lead, they somehow throw it and get thrashed by their opponent. And that’s exactly what has been happening since the previous few seasons. Last season in the Champions League against Real Madrid, they had a good lead but then lost.
And who can forget the infamous Barcelona versus PSG Champions League comeback! PSG is a good team and all, but they are not very strong when it comes to the Champions League. Actually, I am going to say it, they are not going to win the Champions League this season as well.