The former Manchester City striker already scored his first goal for the club during a friendly on Thursday.
"He joined the squad on Thursday, is in good shape physically and I will decide today whether he'll start or be on the bench. It is not just a tactical choice, but also dictated by the situation," said Coach Allegri in his Press conference.
"Mario can consecrate his status definitively as a star at Milan. In other teams he played less than he expected to. In my view he can be paired with Giampaolo Pazzini, who has done well so far this season.
"Balotelli's arrival is important for the club in media terms. He has brought a strong wave of enthusiasm, although we must remain detached from that. Things are going better, we must concentrate on tomorrow's game which will allow us to stay in the race for a Champions League spot.
"I think it's good to maintain a healthy competition for places between the players. I have to put players in the right roles, so this is why I sometimes have to leave out those who would deserve to play."