Thomas Tuchel's side, depleted by a raft of injuries, slumped to a 2-0 loss against Reims on Wednesday which ended an unbeaten 22-match run at the Parc des Princes.
Discounting a handful of defeats after winning the league in previous seasons, it was PSG's first meaningful loss at home since November 2012.
"It was a poor performance. We had a lot of players missing, that's why we made so many changes," said Tuchel.
"I have to manage the playing time of the squad. And I think it was possible to play better with the team we had on the pitch".
PSG remain top of Ligue 1 on goal difference, above surprise second-place side Angers, but defender Marquinhos said they must strive to consistently keep the bar high.