In an astonishing revelation, Ilan - who has scored two in their last two games - claims that Zola is no longer in control and will not be able to win the players back.
Ilan, who arrived on a short-term deal from St Etienne in January, also revealed he was not planning on staying at Upton Park beyond the end of the season.
"I don't want to say bad things about Zola because he is a good person, but you know sometimes a good person working in football doesn't work," Ilan told the News of the World.
"If you give your players a lot of freedom, they will not obey you anymore.
"That is what is happening now at West Ham, especially with players who speak Italian.
"Zola has lost control of the team and it is impossible for him to recover it."
Ilan is not happy with how he is used by Zola.
"Zola never uses me in my position as a centre forward," he said. "He puts me out on the flanks or even as a second forward.
"He and the other coaches in the Premier League have an obsession with putting the players in positions different to the one they are used to."