Ronaldo, 33, joined Juve last month in a club-record transfer after nine trophy-laden years at Real Madrid.
And while much fanfare has surrounded his arrival in Serie A, Alberto Zaccheroni, who managed the Italian giants briefly in 2010 has made the comparison of France legend Michel Platini, who won the Ballon d'Or three times during his five seasons at the club.
"Ronaldo? It's not a given that he'll score so much in Italy. I remember even [Michel] Platini suffered a lot during his first year in Italy," he told Il Mattino.
"The Portuguese will certainly experience some difficulties at the beginning.”
Zaccheroni went on to claim Napoli have 'their own Ronaldo', defending the club's decision not to attempt to lure the Portugal captain to the Stadio San Paolo.
The club's President Aurelio De Laurentiis has faced major criticism from the club's fans for their lack of transfer activity while their league rivals Inter, Milan and AS Roma have invested significantly ahead of the new season.
"Napoli have their own Ronaldo: Carlo Ancelotti," he said. "I was sure that Carlo would choose the Premier League, but instead he chose the project offered to him by De Laurentiis."