ESPN is reporting that, despite the X-rays on Mark Prior's elbow being negative (after Prior left today's game between the Cubs and Rockies in the 4th inning as a result of being hit by a liner up the middle), a subsequent MRI showed a "slight" fracture of the elbow.
No news yet on how long he'll be out, but Prior will almost definitely go onto the d.l. Awful news for the Cubs, and if Prior is gone for long, this pretty much finishes their season.