Jon Lester will start on Tuesday against the Angels. That moves him ahead of Josh Beckett. Beckett last started on Thursday and Lester on Friday.
Terry Francona said the Sox are taking the opportunity to tweak their rotation. He did not directly answer a question about Beckett's health. But this seems to be more matchup based or based on lining up their catchers so that Jason Varitek is not overworked.
UPDATE, 12:15 p.m.: Now hearing that this could possibly be related to a physical issue. More to come after the game, hopefully.