Stout was placed on the 15-day injured list with lower-back discomfort Thursday, Kevin Gorman of TribLive.com reports.
Stout was hit hard during Wednesday's relief appearance against the Yankees, allowing four runs on three hits and a walk while striking out one in one inning. It's possible that the southpaw's back injury contributed to his struggles, and he'll be forced to miss the remainder of the year after landing on the IL. Over 20 relief appearances between the Cubs and Pirates this year, Stout posted a 5.64 ERA and 1.84 WHIP in 22.1 innings.