The Sox placed Dice-K on the 15-day DL and called up Hunter Jones, a lefty reliever, from Pawtucket. I think it's hard to argue that the WBC isn't responsible for Matsuzaka's "arm fatigue," which is what the Sox are calling Dice-K's injury.
I'm not sure who will replace Matsuzaka in the rotation. Clay Buchholz, the most likely replacement, has a hamstring injury. It may be Masterson or Bowden. I'm not sure The Sox calling up Jones signals that Masterson will get the spot. Jones is on his way to Oakland, and Boston needs a reliever after last night's game.