4-4-1-1 with a defensive winger on the right and most probably Marchisio on the left.
That's my prediction (far from being my wish).
Actually, I think we'll see only 2 changes compared to yesterday's match (Grygera for Caceres and Canna for Legro) and perhaps a third change if Trez won't make it, but these won't be tactical changes.
Winning away to Parma and knowing that Ronaldinho operates from the left, makes me believe that Ciro won't dare changing anything. He'll try to close down Milan's biggest threat and the formation from yesterday is what can offer him that.
He proved that he's not flexible (he even kept the winning 4-2-3-1 formation when we played Bordeaux, even though it was never going to work with Del Piero on the wing).
Be prepared for this:
Manninger
Grygera-Cannavaro-Chiellini-Grosso
Salihamidzic-Poulsen-Melo-Marchisio
Diego
Trez/Amauri