Ibrahimovic, whose start to the season was plagued by injuries, had a nice build-up to the game, scoring six goals in four Ligue 1 matches.
But once again, the talismanic Swede disappointed in a big game, failing to fire a shot on target as he lived up to his reputation as a striker who fails to shine on big occasions.
"I would have liked it if we had had more attacking power," Blanc told a news conference.
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"As a coach I am optimistic," the former France coach said.
"Our squad will not change much during the season so I have to everyone, including Zlatan, is good in this kind of matches.
"I have the choice not to make him play, to rest him for 15 days, but I also have the choice to encourage him, to make him work so that he is at his best level in a game like today's, but also in games that will be more decisive later in the season."
Ibrahimovic started up front with Angel Di Maria on his right and Edinson Cavani on the left but he made little impact.
"In the first half we were good in our own half but then we were losing the ball in the midfield," Blanc said.
"After the break we were much better and they started to lose the ball. Indeed we exposed ourselves to counter attacks but that's the price to pay when you want to beat them.
"We wanted to win this game so obviously we are disappointed."
Real Madrid counterpart Rafael Benitez hailed his team's performance.
"We saw an aggressive team, who had a desire to go for the goal," the Spaniard said.
"We brought the danger in their area with Jese, Lucas Vazquez, Cristiano Ronaldo. We lacked that little detail that makes the difference but the overall balance is very very positive."
Real are top of Group A with seven points and lead PSG on goal difference after three games.
(Editing by Ed Osmond)
