Mazza's back recently "locked up again," halting his rehab progress, Adam Berry of MLB.com reports.

EDGE Analysis

Mazza was placed on the injured list April 23 due to back spasms. Though he's eligible to return, he has continued to experience discomfort and his activation does not appear imminent. Prior to being sidelined, Mazza had been hit hard as a bulk reliever, as he has an 11.81 ERA and 2.81 WHIP with a 5:6 K:BB across 5.1 frames.