Ronaldo has been in scintillating form so far this season for both club and country, scoring 33 goals in all competitions, although he has missed Real's last two games with a thigh injury.
The 28-year-old scored a hat-trick in the second leg of Portugal's World Cup play-off with Sweden last month to secure a 4-2 aggregate win and ensure his country's place at the finals.
And, speaking ahead of the World Cup draw in Bahia on Friday, Real assistant Zidane heaped praise on the former Manchester United man for his displays this term.
"What Cristiano (Ronaldo) is doing speaks for itself, there is no need to speak," he said.
"We speak a lot about him at the moment, but what he is doing on the pitch is monstrous.
"The proof for how well he is doing is in the game against Sweden, many people wrote Portugal off and he took the team into his own hands scoring a hat-trick.
"It is the demonstration of what he has been doing and seeing him train every day makes me proud."
Zidane refused to name a favourite for next year's World Cup, but he is hopeful that France - who he helped to triumph in 1998 - will be able to go far in the competition.
"It's never easy to call a favourite at the World Cup, every team is favourite to win the World Cup," he added.
"We've noticed in fact that the gap between European teams and South American teams has been reduced. I can't name a favourite.
"I don't think France we'll be too far away from the group of teams that always goes far in the tournament. I think it will be the usual teams that go far."
