The Juventus forward was a key player under Zidane during the coach's first spell at the club, and he credited the Frenchman with getting the best out of him in that time.
He told DAZN (h/t Goal's Sacha Pisani):
"The confidence that a player needs doesn't only come from himself but also from the players around him and the coach.
"You need to feel like you are an important part of the group and Zidane made me feel special.
"He helped me a lot. I already had a lot of respect for him but working with him made me admire him more.
"That's because of what he's like as a person, how he talks, how he led the team and how he treated me."
Zidane took charge in January 2016 and worked with Ronaldo until they both departed at the end of the 2017-18 season.
During that time, Ronaldo scored 112 goals and laid on 28 assists in 114 appearances.
His contributions played a significant role in the team winning three consecutive UEFA Champions League titles under Zidane, as well as La Liga in 2016-17. Ronaldo also won two of his five Ballons d'Or in that time.
After Zidane returned to the Santiago Bernabeu in March, football journalist Guillem Balague noted the difficulty of the job he faces without Ronaldo to call upon:
So too did beIN Sports' Roberto Rojas:
Roberto Rojas @RobertoRojas97
Zidane could’ve easily said no to Real Madrid after finishing on top with 3 Champions League, now I think is the big challenge for him to show what he is really capable of as a manager to see what he can do with a team going through a rebuilding process post Cristiano Ronaldo.
Zidane took charge of Real with 11 matches remaining in La Liga, the team having already been knocked out of the Champions League and the Copa del Rey. He won just five of those and suffered four defeats.
Even in victory they were defensively poor in a 5-3 win over Fenerbahce, and they only scraped past Red Bull Salzburg 1-0.
It will take time for Zidane to bed in his new signings, as the club have made four first-team acquisitions this summer—Eden Hazard, Luka Jovic, Ferland Mendy and Eder Militao.
Nevertheless, it's clear he has an enormous challenge on his hands to rebuild the team, made all the more difficult without Ronaldo.
If he can give Hazard and Jovic the same confidence he gave to Ronaldo, though, they might be able to make up for his absence between them.