There is a really interesting statistics about this matchup. I checked the head-to-head games and saw that Milan can't defeat Napoli in San Siro in a league game since December 2014. Napoli will have a huge psychological predominance against them as a result. It is up to Milan to put an end to this bad luck. They have a Champions League game to start in ten minutes and getting a win here would motivate them even more for the Napoli game. Milan and Napoli are both doing great in the Serie A now. Maybe it is a risk to take but I'm thinking of betting on Milan win @2.24.
This match is most likely to be a draw. Both the teams are equal in points, and both the teams are performing quite well this season. No one wants to lose their position in the points table by losing points. But I think the team that wins this match will be at the top of the points table for some time.
In the Champions League too, the Napoli team has won well against Liverpool and Rangers. Napoli dominated both matches. AC Milan's performance on the other hand has been very consistent. However, this match may be played by both teams in a defensive strategy. A 1-1 goal could lead to a draw. I will bet on a 1-1 draw.