Ronaldo won his fifth Ballon d'Or, for world player of the year, last week to draw level with his rival and Barcelona forward Lionel Messi.
The debate about who is the greater player is a perennial feature of soccer punditry, but Zidane is convinced he has the world's best at his disposal.
"I have the best in the world and he is showing it in this shirt," Zidane told a news conference in Abu Dhabi on Tuesday. "I am delighted to have him, for me he is the best."
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Madrid face United Arab Emirates league champions Al Jazira on their home soil in the semi-final on Wednesday, with the final on Saturday.
Although Madrid's next La Liga match is a crucial Clasico clash against Barcelona at the Santiago Bernabeu on Dec. 23, Zidane said his squad is fully focused on the inter-continental tournament.
"We will do everything we can to win this competition," he said. "It will not be easy, first we have to get to the final. We're only thinking about winning the Club World Cup.
"There are no easy games. We have a semi final against, a team that people say is easy, but we don’t think that it will be, quite the opposite.
"Look at last year against Kashima (Antlers). Against Real Madrid everybody wants to have a great game and for that we will go out focused."
Madrid won the competition for the first time in 2014 and again last year, when they beat Japanese side Kashima Antlers 4-2 after extra time.
The Spanish champions can become the first side to successfully defend the trophy since the tournament began in 2000 and can pull level with arch-rivals and record winners Barcelona on three victories.
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