Marquinhos offered no excuses for Paris Saint-Germain's "s***" form as he demanded improvement from his team-mates.
PSG have won Ligue 1 but have now tasted victory just once in six matches in all competitions, having followed up a Coupe de France final defeat to Rennes with another late loss against Montpellier on Tuesday.
The champions made numerous individual errors in a poor display in the 3-2 reverse, with coach Thomas Tuchel indicating that a thin squad was feeling the effects of a tough season.
Yet Marquinhos was not interested in explaining away PSG's recent performances, acknowledging that they have to be better.
"This is a difficult, hard time and, in these moments, we have to work," the Brazilian told reporters. "This is the message that I will pass on to the dressing room.
"Football is about a collective. If we do not think for each other, especially in the difficult times, then...
"When all is well, it's easy to go and win matches. But we have responsibilities, we know how big PSG is and how much we are hated by many people and loved by many others. We have to deal with the pressure and stay united if we are to get by.
"This is the most complicated season I've had. We have had some difficult moments before but usually we immediately come through them, raise our heads and come up with answers.
"For a little while now, we have not had answers. We have not played well. There are four games left and we cannot play s*** and keep losing games. We are PSG, we are the champions. We must show something else."