Song will be lost to the Gunners due to Cameroon's African Nations Cup campaign.
But on Nasri, Wenger told arsenal.com: "No, [he is not a replacement].
"I do not say that he could not, Samir is very tactically astute, but he is attracted forwards. He loves the offensive game.
"We have Denilson who can fill that role. He is more suited than Samir at the moment. Samir is more a player who has pace, is versatile around the box and can finish. It would be a sacrifice to put him down there. Also he has a little handicap in the air.
"He likes [that defensive role] and certainly, technically and tactically, he can do it but I believe he can be more efficient up front."