Max Allegri says Napoli are just one of five or six teams that could rival Milan for the title this season.
Milan currently lie four points clear of Napoli at the top of the table.
Speaking to Radio Anch'io lo Sport, Allegri said: "I don't know if it will be like this at the end.
"Napoli are doing important things and, at the moment, they appear to be the most dangerous opponents.
"I think that they will last until the end, but there are other teams in pursuit of the Scudetto and they will give us a hard time until the end of the season. There are five or six title contenders."
Reflecting on Milan's 2-0 victory over Cesena last night, Allegri said: "It was important to get back to winning ways and deservedly so after two draws."
Finally, Allegri gave his first impressions of new signing Urby Emanuelson.
"He is a dynamic player with good technique. Moreover he will be the only left-footed player that we have on the team.
"I think that he is an important signing."