The Italy international hurt his left knee during Sunday's 2-0 loss at Udinese and, though tests ruled out any ligament damage, Gilardino will be out until November.
"I felt a terrible pain," Gilardino said. "I was really afraid I would have torn a ligament but fortunately the injury is less serious than what I first feared.
"I will return to play sooner than I expected."
Without Gilardino, Fiorentina coach Sinisa Mihajlovic will have to rely on Stevan Jovetic and Santiago Silva to deliver in front of goal.
Both players have yet to score this season.
"We created very few goalscoring opportunities against Udinese," Mihajlovic said.
"Although Udinese defended deeply throughout the game, we have to try to be more creative and lethal in front of goal."
Parma, meanwhile, bounced back from their 4-1 defeat at Juventus with a 2-1 win over Chievo in the last round.
Two goals from Sebastian Giovinco handed the Ducale club its first victory of the campaign.
"It's a good victory considering it came against a Chievo side that has pleasantly surprised me," Parma coach Franco Colomba said.
"We played much better than we did against Juve and we deserved this win."
The visitors will be without Giovinco, who serves a one-match ban on Wednesday.
Sergio Floccari is set to play alongside Pelle in Parma's attack.