Woodruff (hamstring) will begin a rehab assignment in the Arizona Rookie League on Saturday, Adam McCalvy of MLB.com reports.
The young pitching phenom has been out since June while recovering from a right hamstring injury, and manager Craig Counsell had already announced he wouldn't be activated until late July. The hard-throwing righty will likely need a few rehab outings before being deemed ready to return to Triple-A Colorado Springs, where he owns a 4.12 ERA over 12 starts this year.