St. Louis placed Liberatore on the 15-day injured list Tuesday with lower-back tightness, Jeff Jones of the Belleville News-Democrat reports.
Liberatore was scheduled to return to the Cardinals rotation Wednesday in Pittsburgh, but the back issue that arose in his previous start Aug. 16 didn't fully respond to a period of extra rest. The young left-hander has struggled to a 6.12 ERA, 1.64 WHIP and 35:21 K:BB across 50 major-league innings this season.