Ibra was suspended for last night's shock defeat to Palermo.
Allegri said: "There's no point talking about how important Ibra is for us, but tonight we should've done more. We have to analyse what didn't work.
"Alexandre Pato and Antonio Cassano were playing as a pair for the first time, so it's natural it'd take a while to settle. I had to look at the full 90 minutes, as Robinho is tired and Kevin-Prince Boateng cannot play a full game at the moment.
"I remain convinced Milan are the favourites for the Scudetto, so even if things go badly, we'll still be two points in front."