It's certainly a race, PSG also needs to stock up on weapons, in this case strong players.
He can't stop because if he stops he will be caught up by the other teams and if he wants to excel he will have to work even harder. This is the live of top level actor.
I think PSG squad is already very solid to compete in this year Champions League so there is no need for them to bring in other expensive quality players into the team because it could damage what has been established so far, but if they want to add players Luis Enrique should focus on a solid reserve goalkeeper or defensive midfielder just to rotate the core players so that the balance is maintained.