The French striker hasn't scored since mid-February and was hooked on the hour mark yesterday.
But Zidane insisted: "I will set my best smile to give you an answer. But I'm not going to say anything.
"I'm not worried, but perhaps he should laugh more on the field. I also laughed little as a player."
He continued: "There are no problems with Benzema. He's doing well. Perhaps others worry, but I do not. Whether he plays on Tuesday? I do not know yet. I have no idea who is going to play. It is the last game before the final of the Champions League. It is now the most important game of the season for us."