As you said though, it could be just them saving everything up to guarantee their qualification. I never understand teams that do this however. Mentality is a habit, not something to switch off and on.
The mentality is really a habit, but the player has a choice: go into a hard collision while fighting for the ball, or remove the foot. During the most important matches, they behave more violently than during simple games. And opponents, knowing this, allow themselves more aggression (in simple games), therefore they have a certain advantage.
This is exactly why I rate players about work rate more than about talent. I admire teams like Dortmund and Liverpool, where the majority of the players were not starting out as people you would say were the most talented players, but they put in large amounts of workrate and mentality that take them to the next level.
Salah and Mane for example, for years nobody would say they had talent and Mane especially, even today after all his achievements no one would put his on the same level as many PSG people or his fellow wingers there. Yet he works so hard and always fights for the ball, when 0-0 or when 5-0 he does the same.
The moment he decides to switch on and off depending on how important the game is will be the moment he fails as a footballer in his coach's vision.
I feel like Neymar switched off after going from Barca. That is perhaps the most expensive blow for PSG. If I'm honest, and I actually really like him, but have never admired him.
