Contreras (forearm) was placed on the 7-day minor-league injured list Tuesday, Mike Persak of the Pittsburgh Post-Gazette reports.
Contreras recently stepped away from Double-A Altoona to be evaluated for forearm tightness, and he'll miss at least a week as a result of the injury. The right-hander has posted a 2.35 ERA and 0.91 WHIP in 46 innings across nine starts with the Double-A club this year, but it's not yet clear when he'll be able to return to action.