Watford coach Gianfranco Zola believes Napoli are Juventus' main obstacle in retaining their Serie A title.
The ex-Azzurri player, who spent four years in Naples as a player, does not think AC Milan or Inter are strong enough to challenge, but feels Roma could also be dark horses in the race for the Scudetto.
"Because Milan did not reinforce and Inter don't seem superior to their status last season, there could be room for teams like Napoli and Roma," the former Chelsea star told Il Mattino.
Milan are currently reeling from the losses of Zlatan Ibrahimovic and Thiago Silva, while Inter have lost long-standing veterans in Maicon and Julio Cesar.
He is also impressed with the form of 21-year-old Lorenzo Insigne, who has come in to fill the void caused by Ezequiel Lavezzi's departure to Paris Saint-Germain.
"I saw him play for Pescara last season. I like him a great deal and hope he has the chance to play and grow at Napoli," stated Zola.