Napoli, who finished second in the table in 2012-13, have invested heavily in their squad this summer under new coach Rafael Benitez.
However, Chiellini has claimed that there are more "realistic challengers" to their league crown next season.
"Napoli have made wholesale changes, they've got a new manager and will play in a different way," Chiellini told the club's official website.
"The likes of Milan, Inter and Fiorentina are slightly ahead of the rest. I view these teams as our most realistic challengers in the Scudetto race."
Chiellini has also admitted that it will be "very difficult" for Juventus to make it three league titles in a row next season.