Justin Masterson underwent an MRI scan today which revealed he has a strained left oblique.

How long he will be out of the rotation is not clear but manager Terry Francona said this:

""He will defintiely miss a start. After that we'll go on symptoms. He can't do anything until he is pain free. So we will go completely on that.''

Masterson was forced to leave Monday's game against the Orioles in the second inning when he felt tightness in his rib cage.

""Everything is going to depend on how I feel'' Masterson said. ""We'll take a couple of days maybe three and then assess what we've got.

""It could be a short time it could take a little while. It's not worse than it was yesterday. I feel it a little when I cough.''