Matthews has a slight tear in his ACL and is out indefinitely. I couldn't be happier. This will force Scioscia to keep Matthews on the pine and insert Rivera or Willits into the lineup on a daily basis for a while.
Rivera had already supplanted Matthews, and put up great numbers in July - with an OBP of .455 and a SLG of .704. But, this will make the move a little less likely to dissolve after a couple of bad games from Rivera or a sudden return to ignorant deference to veterans by Scioscia. It is his most glaring weakness as a manager.
Anyway, I don't love rooting for injury, but as injuries go, this is a net positive for the team on the offensive side of the equation.