The Spaniard believes there could be seven sides battling for the Scudetto this season but has tipped last year's top two as the teams to beat
Benitez enjoyed a promising first season in charge, winning the Coppa Italia and securing Champions League football, although his side finished 24 points behind champions Juventus and seven adrift of Roma.
The Spaniard expects those two clubs to lead the way again in the new campaign, even though Juve have lost the services of Antonio Conte, but also pointed to the threat posed by Inter, who beat Roma 2-0 on Saturday.
"For the Scudetto, Roma and Juventus start with an advantage," Benitez told Sky Sport Italia. "We also saw Inter have constructed a younger team with more intensity.
"All three of them will be difficult to beat, but we mustn't forget Fiorentina and Milan too."
Napoli earned a 2-0 pre-season win over PAOK on Saturday with goals from Jose Callejon and Josip Radosevic.
Benitez was heartened by the display and believes new signing Kalidou Koulibaly, who arrived from Genk in May, will strengthen his side's resolve.
"If we make good signings it is because [director] Riccardo Bigon and his staff work so well," he added.
"Kalidou Koulibaly is a player with the characteristics we were looking for in defence."