Castro (oblique) will begin a rehab assignment with Triple-A St. Paul on Friday, Do-Hyoung Park of MLB.com reports.
Castro was placed on the injured list Aug. 15 and is now set to begin the final stage of his recovery. The Twins haven't indicated how long they plan to keep Castro on assignment, but there's a good chance he returns before the end of August. The 26-year-old utilityman was slashing .235/.323/.383 through 93 plate appearances since the All-Star break prior to getting injured.