Contreras is being examined in Pittsburgh for forearm soreness, Kevin Gorman of TribLive.com reports.
The 21-year-old has stepped away from Double-A Altoona to have the injury evaluated, though GM Ben Cherington believes it to be a minor issue. Contreras has been fantastic in nine starts for Altoona this season with a 2.35 ERA, 0.91 WHIP and 65:11 K:BB over 46 innings.