The Scot released his new autobiography last week, and in the book he revealed that he does not consider the 33-year-old England captain to be a "top, top player".
"For two or three years, Steven Gerrard was the best midfield player in the world," The Mirror quotes Zidane as saying. "Even now he is playing at a high level for Liverpool and England.
"Gerrard has been loyal to Liverpool throughout his career – which is great for them – but if he had wanted to leave four or five years ago then every top club in Europe would have tried to sign him and they would have probably had to break the transfer record to do it.
"Alex Ferguson is obviously one of the most successful coaches the game has ever had, but I did find his comments about Steven Gerrard very strange. To say he is not a top player is wrong."
Gerrard, who has amassed 107 international caps, recently scored his 100th Premier League goal in a 2-2 draw with Newcastle United.