Only one modification to the 3-4-2-1 against Genoa? That should be it for the chosen system by Vincenzo Montella who may have put Zapata in for Musacchio and decided to go for an all-in at midfield and increasing his offensive potential.
Here is Milan's probable line-up against Genoa:
3-4-2-1: G.Donnarumma; Zapata, Bonucci, Rodríguez; Borini, Kessie, Biglia, Bonaventura; Suso, Çalhanoglu; Kalinić.