The Croat has had such an impact since arriving a couple of weeks after Gibson in January that even a couple of games without scoring have raised eyebrows.
Gibson has no concerns though.
"He's a bit like Michael Owen or Van Nistelrooy in the box," the Irishman told evertonfc.com. "He's first class and I don't think there's many better than him in the Premier League at the moment.
"The vein of form he had when he first came was special, and from a football point of view I think we knew he couldn't keep it up constantly.
"Every striker goes through a lean spell but it hasn't taken him too long to score again. He's definitely up there with the best goal scorers I've played with to be honest. His finishing is unbelievable."