Ronaldo, 34, is in his second season with the Old Lady. Having bagged 21 Serie A goals in 2018-2019, he has six to his name from 11 outings this term.
That is slightly below what would be expected of the Portugal international, who has been struggling with a knee injury for a few weeks.
Rumours of a spat between player and coach surfaced a while ago and things seemed to escalate when the former Chelsea boss substituted him in back-to-back fixtures against Lokomotiv Moscow and AC Milan.
Sarri stressed he was trying to protect the former Real Madrid ace due to his knee complaint and he played no part against Atalanta before returning for the 1-0 Champions League victory over Atletico Madrid on November 26.
Ronaldo played the full 90 minutes as Juve drew 2-2 with Sassuolo on Sunday to surrender top spot in the Italian top-flight standings to Inter.
The Turin outfit have worthy challengers this time around in the form of the San Siro giants and will need to be pulling in the same direction to get the job done – something Cassano is adamant is not happening at present.
“I think Ronaldo has a big problem with Sarri,” he told told Tiki Taka. “Everything started with two consecutive substitutions, which will irritate any player.
“In my opinion, there’s a problem between them and Juventus are good at keeping it down.”