The All Blacks have already lost star fly-half Dan Carter to a tournament-ending groin injury and McCaw has been struggling with a foot injury.
But, after pulling out of two pool matches, McCaw insisted he would be "good to go" against the Pumas at Eden Park.
"The foot feels good after a bit of rest last week and over the weekend," said McCaw.
"I trained with the team yesterday and it is always hard when you have missed training here and there.
"I would like to think that, when you have been playing this game for a few years, you know what you need to do to get in form.
"I've just got to make sure I get into form and that's the key. I am confident and all the boys are in pretty good shape.
"The boys are excited. I suppose there are a few nerves because we are at the business end, but there are lots of excitement, too. The boys can't wait to get stuck into it."