The 32-year-old forward has helped Los Blancos win three Champions League crowns and two La Liga titles since arriving at the Santiago Bernabeu from Old Trafford in 2009.
However, his future at Real came under question last summer and speculation has resurfaced in recent days amid a disappointing season in which the Portugal international has only scored four goals in 14 La Liga appearances.
Earlier this week, AS reported Ronaldo wants to leave the Santiago Bernabeu and rejoin United after "feeling betrayed" by club president Florentino Perez over a broken promise of a pay rise.
The Spanish publication said that Ronaldo is currently earning €21m (£18.6m, $25.7m) per season – the equivalent to £360,000-a-week – and believes his deal should now be upgraded after Lionel Messi recently signed a new deal worth €50m-a-season at Barcelona.
Neymar is also earning a similar fee at Paris Saint-Germain and El Mundo later added the former United star believes that his current deal shows "a lack of respect," given he has been crowned the best player on the planet the last two years running.
Furthermore, El Mundo added that Ronaldo believes these disagreements are affecting his performance and blames Real for his current form.
It has been said that Real president Perez doesn't plan to hand Ronaldo a new deal and would even be ready to negotiate his departure for the right price in order to fund the potential arrival of Neymar from Paris Saint-Germain.
Portuguese publication Record says that Perez has already told Ronaldo's agent Jorge Mendes to bring him offers from other clubs ahead of a potential exit.
Zidane is well aware of those reports but the Real boss still expects his star to continue at the Santiago Bernabeu in the long-term.
"We know what people are saying, but what Cristiano has to do is think about playing, like he always does. I just want to talk about his performance and what he can bring to the team on the field. Cristiano is at his club, where he should be. The club, the fans and everyone loves him. I always say the same, I can't imagine Real Madrid without Cristiano," Zidane said ahead if the first leg of the Copa del Rey quarter-final clash against Leganes.
"The footballing side is what interests me the most. People are talking about this at a difficult time for the team, but we still believe that things are going to change.
"I don't want to talk about the contract or things like that. Cristiano can do that and it's him and the club who should talk about that. What I talk to Cristiano about are on-field matters. It's better for everyone. Those upstairs manage it and I don't get involved."
Zidane may be powerless to stop Ronaldo's exit amid suggestions that he could be sacked if he fails to turn around their current situation at the club, with Los Blancos 19 points behind Barcelona in the La Liga table
"I don't overthink anything, I live day to day and I'll not change that," Zidane replied when asked about his own future at Real. "The situation is what it is today. In the two years that I have been here, when we have won a lot, I've always said the same thing. I know the situation and what this club is like and I always go day to day."