Diaz was diagnosed with a left forearm contusion after exiting Sunday's game against the Diamondbacks, Tricia Whitaker of Bally Sports Sun reports.
Diaz was hit by a pitch to lead off the bottom of the first inning and attempted to stay in to run the bases, but it wasn't long before he was replaced by a pinch runner. The 33-year-old appears to have avoided a fracture and should be considered day-to-day heading into Monday's series opener at Oakland.