Valencia's MRI Friday confirmed the initial diagnosis of a mild-to-moderate hamstring strain, the San Francisco Chronicle's Susan Slusser reports.
This confirms what was already widely acknowledged, although the A's have still not released a timetable for Valencia's return. He will be out at least 15 days, and Chris Coghlan and, to a lesser extent, Jed Lowrie, will presumably get the bulk of the at-bats at third base in the meantime.