With some apparent reluctance, Jorge Posada has thrown his glove into the Yankees' rotating first-base mix. The Yankees have six games in National League parks approaching on their schedule, which has prompted the club to entertain trying Posada as a makeshift first baseman in games that Mike Mussina pitches. The concept would allow understudy Wil Nieves to continue catching the right-hander while keeping Posada's bat in the lineup. Posada has appeared before in Major League games as a first baseman and was signed as an infielder, so the change is not completely foreign. That won't make it simpler, Posada said. "When you're behind the plate and you've been behind the plate for so long, things come instantly," Posada said. "When you're at first base, you have to think where you're going to be at. Instincts don't play a role here. It's not going to come easy." Yankees manager Joe Torre characterized the chance of Posada seeing action in the infield as "possible," and his first assignment could come at Colorado on Tuesday, when Mussina takes on the Rockies.