Gianluigi Buffon has predicted a difficult season for defending Serie A champions Juventus after Italian rivals AC Milan, Roma, Inter and Napoli all strengthened.

Juventus are seeking a seventh successive Scudetto in 2017-18 but are set to come up against improved opposition in Milan, Roma, Inter and Napoli.

Milan have been the most active, raiding Juventus for Leonardo Bonucci, while signing Lucas Biglia, Andre Silva, Hakan Calhanoglu, Andrea Conti, Ricardo Rodriguez, Mateo Musacchio, Franck Kessie and Fabio Borini.

Rick Karsdorp, Cengiz Under, Aleksandar Kolarov, Maxime Gonalons, Lorenzo Pellegrini and Hector Moreno have joined Roma, Inter have recruited the likes of Borja Valero and Milan Skriniar, while Napoli have retained their stars after finishing third last season.

Speaking after Juve's penalty shoot-out win over Roma at the International Champions Cup on Sunday, captain Buffon said: "It was a good tour of the US and important for us to find our form towards the start of the season.

"It'll be very difficult for Juventus this year, because many teams have strengthened, such as Roma, Inter and Milan, while Napoli kept their stars.

"Juve believe in our capabilities, though, in the values that brought us success and think we can still give our best."

Juve have also been busy in the transfer market, bringing in Federico Bernardeschi, Douglas Costa, Wojciech Szczesny, Mattia De Sciglio and Rodrigo Bentancur, while they also permanently signed Juan Cuadrado and Medhi Benatia.

Buffon and Juve face Tottenham in London on Saturday before clashing with Lazio in the Supercoppa Italiana on August 13.