Zidane says Bale's talent is worthy of a world record price-tag.
He said: "This is modern football. You have to pay to get the best players in Europe.
"Last season Gareth was on the same level as Ronaldo and Messi. The best players can have not so great games but change a game with a moment of brilliance.
"Those are the sort of players that win you Champions League and league titles.
"He is already one of the finest players in Europe and he has everything needed to become the best player in the world.
"It is a bit of a cliche but it is true you become a better player playing with better players."