If you've read this site in the past 10 seconds, you'll know that Jay Glazer has reported that McNabb is already out for the Saints game. With conflicting reports from Glazer and Westbrook, I'd have to side with Westbrook. (Also, Westbrook is backing up what I've been saying, so I'm furthering my own cause as well.)
Westbrook cracked a rib last year, so he knows what kind of pain McNabb is in. However, Westbrook missed a game last year because of that injury. Really that doesn't mean a whole lot because 1) McNabb is a bit tougher than B-West (if we're being completely frank) and 2) McNabb is not taking a beating every time he touches the ball like Westy would have been.
Again, my assumption is that McNabb will play, and this backs that up. McNabb must have told Westbrook that he plans on playing, and unless McNabb were to fall funny at home this week (considering there's no way in hell he actually practices), he's going to suit up.