Thielbar (oblique) is slated to begin a rehab assignment Tuesday with Triple-A St. Paul, Do-Hyoung Park of MLB.com reports.
Thielbar should be cleared to return to the Twins' bullpen after just a couple of tuneup outings at the Triple-A level. He was sporting a shiny 1.80 ERA through 11 appearances this season with Minnesota when he suffered a right oblique strain in early May.