The Twins selected De Leon's contract from Triple-A St. Paul on Tuesday, Do-Hyoung Park of MLB.com reports.
De Leon last pitched in the majors in 2021 with the Reds, recording an 8.35 ERA and 1.80 WHIP through 18.1 frames. He's done much better this season in the minors (3.62 ERA, 1.37 WHIP) and will take the place of Jorge Alcala (forearm), who landed on the injured list Tuesday.