Hildenberger (arm) was activated from the 7-day injured list Tuesday, Brandon Warne of ZoneCoverage.com reports.
Hildenberger was placed on the MiLB injured list in mid-June due to a right flexor mass strain, but after finishing up a rehab assignment in the Gulf Coast League, he'll return to Triple-A Rochester, where he's posted an 8.44 ERA and 1.96 WHIP with nine strikeouts over 10.2 innings this season.