Ezequiel Lavezzi scored the only goal of the game on Friday as PSG failed to convert a number of meaningful chances to put the game beyond doubt, with Cavani labouring in front of goal alongside Zlatan Ibrahimovic.
Cavani's future has been in doubt of late after he was suspended by the club for arriving back late to training from PSG's winter break, while Blanc stressed before the match the need for the former Napoli star to improve his understanding with Ibrahimovic.
And the former defender concedes the duo did not perform well together on the night at Parc des Princes, prompting him to haul off the Uruguayan in favour of Lucas Moura mid-way through the second half.
"Yes, I had an exchange with Cavani. I had the same with Adrien Rabiot," he told a press conference.
"It is a little personal, but I told him I found what he did to be insufficient and that is why I made the decision to take him off.
"Today their relationship [Cavani and Ibrahimovic] was not good. This is one of the reasons I took Edi off. I thought I had an advantage on the bench with Lucas and that he would have space."
Blanc accepts that PSG fans are entitled to a more ruthless standard of play from the French champions but insists their title defence remains on track.
"We would have liked a much bigger victory. Offensively, we expect much more," he added.
"The fans think we will crush opponents and that each game will be like that. We would also like this type of game, but it's not the case.
"Collectively and individually, it was not as good as Saint-Etienne. But given the timing, we can't all play with the same team.
"They say PSG are not convincing but we are one point behind Lyon before they go to Monaco. We are still there, even without playing well."
