The 5-0 thumping has cast fresh doubt on De Zerbi's position.
The Italian said afterwards: "It's a period... we played well against Rennes and Lens, then we fell into total despair. Once again, I apologize to the fans.
"I'll talk to (director Mehdi) Benatia and (president Pablo) Longoria to understand what we can do. Because these defeats hurt: especially in Paris, especially like this."
De Zerbi continued: "I'm not in the players' heads.
"I don't know what's going on. We prepared for the match as much as possible, but clearly we didn't prepare well: we need to understand why.
"Why do we go to Bruges and play a match like that? Why do we come here and play a match like that? And why do we play completely different matches against Lens and Rennes?"
He added, "When so many players played poorly, there are no regrets. There's no need to talk when you lose like that. You have to look inside yourself and think that you could have done better."