Montpellier won 2-1 at Parc des Princes to advance to the last 16 and while Blanc said defeat was not deserved, he agreed that his team were not at their best.
"I do not have to blame the players for much," Inside Futbol quotes Blanc as saying. "But this is the cup and Montpellier had reason to believe.
"It is a disappointment, but it is not disillusionment. We did not do what we were supposed to do and got punished. This defeat was not necessarily deserved, even though we did not play a very good game."
PSG are currently five points clear at the top of Ligue 1.