PSG confirmed Ibrahimovic sustained a partial tear to a rib muscle during the club's 2-0 win over Bastia in Ligue 1 last week.
The Sweden international, along with team-mate Gregory van der Wiel (knee), will sit out the French champion's fixture at the Parc des Sports but should be back to full fitness in the coming weeks.
"The injuries... I can only tell you what I know for sure," Blanc told reporters.
"Neither Gregory van der Wiel nor Zlatan Ibrahimovic will be in the squad because they simply can't play.
"They have annoying injuries but I feel they won't be unavailable for a long time this season."
In better news for PSG, midfielder Thiago Motta has been declared fit to face Evian, despite suffering a broken nose against Bastia.
Motta was headbutted by Bastia opponent Brandao in the tunnel after the match last week.
The ugly incident saw Brandao provisionally suspended until September 18 by the disciplinary committee of the Ligue de Football Professionnel on Thursday.
But Blanc insisted Motta is good to go for Saturday's clash.
"Thiago Motta is able to play without any issue," said the Frenchman.
"The day after the game, we told you he had a minor fracture. It's not uncommon for players to suffer that type of injury and when it's not a major fracture you can play again quickly.
"He trained immediately after, he has trained all week. He is able to play. He will be in the squad."
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