PSG can afford to play without Mppape, since they have a strong list of players.
Atalanta has lost a very decent one in this period (see below)
I don't think PSG don't feel pressure with the injury of Mppabe and without him, Neymar and Icardi will have to play more. The higher pressure will be put on Neymar, who spent a few years in PSG but has not yet demonstrated his key player role for PSG. He lost in important matches or got serious injuries in most important periods of some seasons.
Atalanta did not have good forms in a few latest matches of Serie A. Maybe it is because of their less motivation to play or is a signal of something bad like overloads. If the later is true, they will get troubles with PSG. I dunno.
I think PSG must feel pressure without the presence of Mppabe, although PSG still has many substitute players. But Mppabe is like a soul for PSG,
I agree Neymar has high pressure because it has not contributed to PSG, therefore with such internal conditions. I am sure that Atalanta will be
able to win against PSG, because Atalanta will play without any burden. Although Atalanta's last game in Serie A was not too good. But not the
guarantee of Atalanta will play poorly against PSG.
PSG won 22 of 27 matches played in Ligue1 (loss only 3 times).
Meanwhile Icardi and Neymar scored respectively 12 and 13 Goals (Mbappè 18 Goals).
Yes for sure Mbappè is a strong player, but in a massive team like this I will not be focused just in one player.
As I have remembered and also @tomahawk9 reported, Atalanta is still missing the man that scored 4 (FOUR) goals in Valencia match.
Ok probably isn't very simple for PSG , but It wouldn't be a surprise if they will pass to the next turn... however they are playing friendly from a while so they have already adapted their workload for this match...