PSG's job looks really difficult this season surely. That embarrassing loss against Newcastle in the Champions League made me think that it will be even more challenging for PSG to qualify for last 16 stage. Milan should be even tougher to defeat for PSG on paper. Seeing PSG in the Europa League would be devastating for the fans.
I even doubt their chance to win the Ligue 1 title for now. Because they aren't so different here either. They play their league matches really inconsistently. They win 4-0 against Marseille but can't even score against Clermont for example. Monaco and Nice are taking advantage of the situation for now. Maybe we can see a new champion this season.
Their defeat doesn't have much impact on the current probabilities as they remain the favorites to qualify, it's just that they have to be extra in the next few matches and don't let them back down. This is only 2 matches and there are still 4 matches left for each club including PSG. In terms of position, they are still perched in 2nd place because it is fortunate that Milan and Dortmund played a draw.
They are still the strongest candidate to qualify for the group phase, it's just that their efforts must now be greater if they really want to qualify comfortably, especially with the acquisition of points that are still very close so that once they lose again then this becomes bad.