The French champions lost 3-1 to AS Monaco in Ligue 1 on Saturday, their third loss in seven top flight matches.
PSG were without Lionel Messi, Kylian Mbappe and Marco Verratti at the Stade Louis II while Achraf Hakiki and Sergio Ramos started from the bench.
The PSG camp have been disturbed by a virus bug in recent days but the defeat angered the club's fans so much so that Presnel Kimpembe had to apologise to them right inside the stadium by using a megaphone after the game.
While PSG struggled against Monaco, Bayern Munich dispatched Bochum in the Bundesliga.
Messi looks likely to return against the German champions but even with the World Cup winner's return, Galtier is worried by his side's form.
"There was a lack of intensity. It is the current state of the team. I can't hide behind that," he said in a press conference.
"The state of the team is like this. It is strange but true. It is bizarre to say that as a PSG manager, but it is the current reality.
"I am worried about the match on Tuesday night. If I wasn't that'd be something serious. We'll see if some of those that couldn't start the match will be able to play on Tuesday.
"We have a very weakened team and we're worried. In this period, you have to stay clear-headed. I understand the fan's anger. There is anger."
