L'Equipe says Zidane held crunch talks with Ronaldo after the Euros in 2016, when he returned for preseason training carrying a knee injury.
Zidane spoke to Ronaldo about his long-term fitness and managed to convince the No7 that he didn't need to play in every game.
"If you listen to me, if you agree to rest from time to time, miss some games, if you trust me, you will extend your career for several years," the Frenchman told Ronaldo.
After consideration, the Portugal captain agreed, which has seen him saved for Real's biggest games over the past two seasons.
And while there has been doubts about Ronaldo's form this term, he has managed to score in every Champions League game this season. He has also scored 21 goals in the last eleven games.