The former Bayern Munich striker is facing over a month on the sidelines after picking up a knee injury against Cagliari, while Juan Cuadrado dislocated his shoulder
The 28-year-old collided with Rossoblu goalkeeper Michael Agazzi during the 1-1 draw, with Borja Valero giving the hosts the lead before Mauricio Pinilla levelled late on. David Pizarro was sent off for Vincenzo Montella's men.
And the Viola announced on Monday afternoon that the Germany international is set for a lengthy absence following further tests.
A statement read: "ACF Fiorentina announces that the investigations carried out earlier today to the footballer Mario Gomez have confirmed a lesion distractive second degree medial collateral ligament of the knee.
"He will be assigned a specific tutor for two weeks and then the athlete will begin a rehabilitation program for the gradual resumption of sports, with an overall prognosis of 6-7 weeks."
Meanwhile, Viola winger Juan Cuadrado also picked up an injury, dislocating his shoulder but Manzuoli is less concerned about the Colombian.
He said: “As for Cuadrado, it’s not an injury that occurs often in football.
"He can be back in the side within a couple of weeks, perhaps even less. It can be painful to the shoulder, but does not take long to recover from."
Fiorentina boss Montella told Sky Sport Italia: “The injuries are certainly the saddest note of the day, so we can only hope they prove to be less serious than they seem."
The Viola are third following the point while Cagliari are eighth.