Japan coach Alberto Zaccheroni sees Napoli as a title threat.

Zacc has coached both Inter and AC Milan during his career.

"A lot of people are underestimating this Napoli, but I wouldn't make that mistake," he said.

"Napoli don't have the same squad strength as others, but if Inter and Milan don't take advantage of theirs then Napoli could profit."

Napoli's Scudetto hopes were boosted by Juventus' 1-0 defeat of rivals Inter in the Derby d'Italia on Sunday evening.

"Although Milan and Napoli are doing well, the championship is still open to Inter," Zaccheroni continued.

"Juventus? Last night's side were a much more compact one than they have been, but the difficulty is keeping this compactness against smaller and weaker clubs."