Thomas Tuchel admitted he was "very surprised" by leaked footage that showed Paris Saint-Germain's players partying into the early hours of the morning this week.
A number of PSG's first-team stars attended a lavish joint-birthday party for Edinson Cavani, Mauro Icardi and Angel Di Maria in Paris on Thursday.
The extravagant bash was held two days after the French champions' 2-1 loss to Borussia Dortmund in the first leg of their Champions League last-16 tie.
Angel Di Maria and Edinson Cavani had a joint birthday party last night 🥳— Goal (@goal) February 21, 2020
They certainly enjoyed themselves 😂pic.twitter.com/volfMMrooo
Footage on social media showed some players, including forward Neymar, topless and bouncing around the room.
And with a Ligue 1 clash against Bordeaux to come on Sunday, Tuchel has questioned the actions of his players.
"I was really surprised yesterday afternoon when watching the video," he said at Saturday's pre-match news conference.
"You can be sure that we talked internally. I don't want to talk about it now, but we talked about it within the club and it has to stay that way."
He added: "You can be sure that we are not happy with this image. We talked together as a team and it is now an internal matter.
"I am here to improve my group. I cannot give advice to the club, that is not my role."
Marquinhos was in attendance at the exclusive Pavillon Dauphine and defended the decision to throw the triple birthday party.
"The leaked footage was a mistake," he told reporters. "However, it had been planned for a long time. We needed to get together.
"We must be careful, though, as there are people who travel miles to follow us.
"There has been frustration at the result and poor performance [against Dortmund]. We know our strengths, especially at home.We must work hard and with a good mentality."
Neymar suggested after the loss to Dortmund that he has been unhappy with PSG's management of his rib injury, insisting he was ready to return to action earlier.
However, Tuchel has reiterated that he cannot risk the Brazil international's fitness at a key point in the season.
"As I said before, it was a discussion between the club, medical staff and myself. With each injury we have to make many decisions, that's the way it is," he said.
"Imagine if we let him play, the injury got worse and he was out for three months. You would have asked the same questions, whether it was a mistake to play him.
"We have to think about why we are making these decisions and you have to trust me. We have talked a lot and it is the same with every player.
"Obviously I want him to play every game and we have to make decisions together. This is the decision we made between us. Now he needs to regain his rhythm."
Tuchel also confirmed Thomas Meunier and Colin Dagba are out of Sunday's clash with Bordeaux at the Parc des Princes, where he is hoping for a quick response from his side.
"It is never easy to start again after a defeat, but that is the challenge," he said. "I have the impression that all the players want to prove themselves.
"Sometimes the players are more competitive when things aren't comfortable. That is exactly the mindset we are looking for."