Penny received an anti-inflammatory shot in the area of the injury on Saturday morning. The club hopes he can resume throwing in approximately 7-10 days, and be back on the mound in a game in 15 days.
"Right now, we think it'll be a minimal stay on the 15-day [DL]," Mozeliak said on Saturday morning. "That's what we're hopeful of."
Penny said he first felt the injury after he pitched last weekend in Cincinnati, and that he aggravated it while pitching on Friday night against the Angels.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.