Real need a win on Tuesday at the Stade Velodrome if they are to top Group C, while a draw would be enough to see them through to the last 16, and Benzema could play his part in his team's qualification.
The France striker, who has been criticised in Spain for his problems settling at Real, scored once in a 4-2 win against Almeria on Saturday and showed at a news conference that he had started to learn Spanish.
"We will see tomorrow when I unveil my starting line-up if Karim plays," Pellegrini told a news conference. "He is a young player who just joined last summer and had to settle and learn a new language. I think he achieved that.
"If he plays, I hope we will see a great Benzema."
"I think he is doing just fine in adjusting (to Real)," Diarra said. "I am convinced the best is yet to come for him."
