I'm not someone who is worried about PSG in the group phase, but losing 4-1 to Newcastle is a sign that PSG has not yet found its best performance under Luis Enrique. PSG won against Dortmund and Milan mainly because they played at home, but then PSG lost to Milan away from home. If PSG can play better at home, then there is a possibility for them to win the game against Newcastle and maybe lose again or drop points against Dortmund on the away game.
So far I am only confident that PSG can qualify for the round of 16 with a total of 9 - 10 points, but it is possible for PSG to lead the standings if they manage to win the remaining 2 matches against Newcastle and Dortmund. Newcastle, however, does not have a high probability of winning the next two matches, but they can threaten anyone who underestimates them, including PSG and Milan.
Luis Enrique put his reputation on the line to get PSG through the group stage, and Eddie Howe squad are their arch-rivals in Group F. PSG must put their previous defeat behind them and focus on securing a place in the last 16, and Newcastle are also targeting them even though the chances are slim. However, if the match ends in a draw then the situation will become more complicated, because both teams will still be struggling to qualify on match day 6, this is the worst scenario for Group F.
I think a draw is very likely, so PSG chances of getting revenge will disappear. Not without reason, Newcastle could give a surprise, and luck might be on their side again. Their victory over Chelsea was more impressive than PSG victory over Monaco in my opinion.
Apart from that, I don't think Milan will be able to beat Dortmund. This is a difficult reality to accept, because Milan has lost several key players. However, it is not impossible that Dortmund will have a bad day and can make Milan lucky to get three points in front of their own fans.