"(Dejan) Stankovic will not recover for the derby. If he has to undergo an operation, we risk losing him for three months," confessed the Coach.
Olivier Dacourt is out for the season after damaging knee ligaments, while Luis Figo and Patrick Vieira hope to be back to full training in January.
Stankovic has been struggling with a heel problem for several months and the recurring injury could require surgical intervention.
"I was counting on having him back this week, but that has not been the case. I hope he'll be at the team's disposal after Christmas."
While Inter patron Moratti continues to insist there is no need to bring in January signings to an already vast squad, Mancini disagrees.
"If Stankovic needs surgery, then we will have to make more than a few little changes to the side."