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."
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."
