8:17pm: Rosenthal tweets that Posada sat out with back stiffness tonight, which contradicts what Cashman said on the air, that this was not injury related.
7:31pm: Mired in a season-long slump, Jorge Posada pulled himself from tonight's lineup according to Yankees GM Brian Cashman on the FOX Saturday Night broadcast. Posada had been penciled into the ninth spot in the order for the first time in 12 years, and ESPN's Buster Olney says (on Twitter) that he refused to play for that reason. He has given no indication that he's retiring.
Ken Rosenthal of FOX Sports and Joel Sherman of The New York Post note that Posada may be in breach of his contract, and that the team could dock him pay (all Twitter links). The Yankees could also attempt to terminate his contract, which has approximately $11MM left on it this season. That will be met with reaction from the union, however.
Posada, 39, is in his first season as a full-time DH. He is hitting .165/.272/.349 with six homers in 125 plate appearances, primarily batting seventh.