The Old Lady were crowned Italian champions last season, and will return to Europe's premier club competition following a two-year hiatus.
Despite the Turin giants enjoying a strong transfer campaign thus far, Cannavaro still believes Antonio Conte's outfit will need more time before European success returns to the club.
"Even with the new acquisitions, Juventus still are a level below Manchester United, Bayern Munich and Real Madrid," the World Cup winner lamented to Tuttosport.
"Their return next season will coincide with getting a taste of European action again, before they can realistically think about becoming champions there."
The likes of Conte, Leonardo Bonucci and Simone Pepe currently face the prospect of bans after becoming implicated in investigations surrounding a domestic betting scandal, but Cannavaro is confident Juventus will be able to cope all the same.
"Conte's absence will be heavy, but the group at Juventus have been tested before. Thanks to the experience of his men, I am sure he will not be missed.
"[Salvatore] Bocchetti will be an excellent replacement for Bonucci. He has enjoyed an excellent spell in Russia, and could make an excellent signing for the club."
Cannavaro, 38, enjoyed two spells playing in the Bianconeri's colours, before retiring from football with UAE side Al Ahli in 2010.
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