Mourinho is already under pressure as United have suffered back-to-back defeats in the Premier League to Brighton and Tottenham.
On Friday, Mourinho fiercely defended his record, claiming that he is still one of the greatest managers in the world.
Zidane, meanwhile, is currently out of work after resigning as Real Madrid boss after the end of last season.
Earlier this month, reports in France claimed that Zidane is targeting the Premier League as his next destination and would be keen on replacing Mourinho as United manager.
But when asked by La Gazzetta dello Sport if he felt Zidane could replace Mourinho at United, Ronaldo replied: I dont know whats happening in Manchester, but wait before criticising Mourinho.
Hes special and hes won a lot.
The two-time World Cup-winning striker also warned Juventus, who will face United in the Champions League group stage, that signing Cristiano Ronaldo will not guarantee them success in Europe.
[Juventus] are a really strong side, said the 41-year-old.
Theyve reached the final twice recently and Ronaldo is going to strengthen them, but the Champions League is not easy. Signing Ronaldo doesnt automatically mean you win it.
What you cannot deny is that its a huge signing – unthinkable – but nobody can predict what will happen and how the balance will change.
I wish him all the best. He will see what a beautiful country hes arrived in, and I love Italy. Hes going to enjoy a great adventure.
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