In his recently-released book, the former Manchester United boss claimed that Gerrard has never been a "top, top player", sparking much debate throughout football.
Zidane, who is now sporting director at Real Madrid, dismissed Ferguson's assertion, hailing Gerrard as the world's finest midfielder in his prime.
"For two or three years, Steven Gerrard was the best midfielder in the world. Even now he is playing at a high level for Liverpool and England," Zidane told the Sunday Mirror.
"Gerrard has been loyal to Liverpool throughout his career - but if he 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."
Owen Hargreaves also came under fire in Ferguson's book, but the former United midfielder was quick to reject the claims that he "opted for the easy options in training".
"Anyone who knows me knows that professionalism is probably one of my strongest traits. A lot of people who rang me this week are very surprised at what he said," he said.
"I had one very successful season, but after the treatment that summer, I virtually never played again.
"My only regret was that I didn't go to him, but I didn't realise the severity of it until it was too late."