In fact, ESPN's Pedro Gomez said yesterday during the Dominican Republic's game against Panama that the real feeling is that Ortiz simply doesn't want to embarrass himself or cost his team a game by making a mistake at first base.
Manager Felipe Alou had hoped to play Ortiz there so he could use Jose Reyes at shortstop and Hanley Ramirez at DH, or vice versa.
You can make a strong case for this argument because, as Newsday's Jim Baumbach astutely responded to a comment of mine on his Final Score blog, if Ortiz were really hurt, "wouldn't the Red Sox be on the phone saying DON'T PLAY!!!"
I can't argue with the decision by Ortiz, but why not just admit it? We all know he can't play the field at all, it's no secret.