Benzema was on the scoresheet for Real's 1-1 draw at Champions League opponents AC Milan last night, but has appeared isolated due to his lack of Spanish.
Comparing Benzema with former Real striker Nicolas Anelka, now of Chelsea, Casillas argued: "Karim is well. All the stories are c***. He is twenty-one years old and plays for Real Madrid. Why do you think he has problems?
"He's great no matter what!
"Nicolas (Anelka) had a special way of being and seeing football. This was not a bad guy, but it was a complicated time, and more with this label as the most expensive player in history. All eyes were fixed on him.
"Karim has nothing to do with him. I think he will become, in one or two years, one of the best footballers in the world."