Niemann will be sidelined for 2013 after a medical exam turned up abnormalities in the labrum and rotator cuff of this throwing shoulder, MLB.com reported.
Niemann, who went 36-21 as a starter for the Rays over his first three full major league seasons, managed only eight appearances last year as he battled a fractured right fibula and shoulder issues.
He was slated for a long relief role this season after bowing to Roberto Hernandez for Tampa Bay's final rotation spot.
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