The result also brought up a fourth loss in their last six matches in all competitions.

"The way we lost is not acceptable at this level of competition," Pochettino said.

Wissam Ben Yedder scored twice for the hosts, flicking in a near-post cross and converting a late penalty as he moved two goals clear of PSG's Kylian Mbappe as the top goalscorer in Ligue 1 with 17 goals.

In between, he created Monaco's second, with Kevin Volland turning his shot past the wrong-footed PSG keeper Gianluigi Donnarumma, with Pochettino clearly angered by the manner of his team's collapse.

It also followed their recent exit in the last 16 of the Champions League, letting slip a 2-0 aggregate lead to lose 3-2 at Real Madrid.

"We can't start a game the way we started this one," added Pochettino. "You have to get out of the frustration of elimination in the Champions League. You have to think about giving the best of yourself.

"We lacked the fighting spirit against a team that wanted to react after being eliminated [from the Europa League].

"It's unacceptable to start the match like that. There is sporting shame. It can't be repeated. We can still lose matches, but what happened shouldn't - and can't happen again because it's serious.

"The spirit and the performance must be collective. We must stop looking for excuses and finding pretexts."

Neymar was one of several under-performing stars to be substituted by PSG boss Pochettino

PSG had not been beaten by three goals or more since their 5-1 defeat to Lille in April 2019

With Lionel Messi absent due to illness, Mbappe provided PSG's only real threat. But he had few chances to impress as the players behind him were out-fought and out-thought by their, seemingly, more motivated opponents.

"We could win 8-0 and nobody would care, they'd just be thinking about the Champions League," Mbappe said. "We need to remain professional, think of our families."

PSG captain Marquinhos described the defeat as a wake-up call. "If we carry on like that the title will be in danger. We have been warned," he added.

"We came here to win and have fun, but that was a catastrophe."

PSG still remain well clear at the top of the table with 65 points from 29 games, 15 points ahead of Rennes, and also Marseille and Nice, who meet later on Sunday. Monaco move up to seventh on 44 points.