From the mouth of Antonio: "People keep asking me about this, but I don’t know anything about it … But the way this man works, he will literally call me the night before and say, ‘Let’s do this movie.’ And I will do it. I’ve done six movies with him, and that is the way he works."
Mr. Banderas (who’s been asked the question a bunch of time on his "Shrek the Third" publicity tour) didn’t appear in the first "Sin City," so I’m wondering where all of these rumors (suddenly) came from. The actor expresses a lot of affection for the filmmaker who helped make him a movie star ("I would follow Robert Rodriguez into hell if he asked me to do it.") and says he’d definitely sign on for the sequel should the director need his help.
Source: Sci-Fi Wire