After scoring PSG's opening goal in Saturday's 2-2 draw with Caen in Ligue 1, the Swede took off his shirt to reveal his tattooed torso.
Ibrahimovic picked up a booking for the celebration, although he explained on Sunday that the removable tattoos were the names of people around the world suffering from hunger.
The campaign is being organised by the UN's World Food Programme.
Blanc said: "I knew he was involved with them but I personally wasn't aware of the tattoos. I knew there was something planned for after the match but that's all.
"He scored very early on and took off his shirt. If it was to show off his tattoos we certainly saw them and it was a successful initiative. But it cost us a yellow card.
"Imagine if the match had heated up and he got a second yellow. The intention was good, but I don't know if it was a good thing to take off his shirt.
"I hope he doesn't do it again tomorrow," added Blanc on the eve of PSG's Champions League last 16, first leg against Chelsea at the Parc des Princes.