Mountcastle (shoulder) is out of the lineup Thursday against the Rays.
Mountcastle exited Wednesday's 1-0 loss to the Cardinals after feeling his left shoulder pop during a swing in the first inning. He's slated to get an MRI later Thursday, at which time more details about the severity of his injury should be available. The Orioles called up outfielder Heston Kjerstad from Triple-A Norfolk to give the team an extra healthy bat in the short term.