De Leon is slated to be added to the major-league roster Saturday now that Triple-A Durham's season has ended, Juan Toribio of MLB.com reports.
De Leon was up briefly for the Rays in August, generating a 3.00 ERA across three innings over a pair of appearances. The right-hander made a successful return from Tommy John surgery this season at the Triple-A level, posting a 2-1 record, 3.51 ERA, 1.33 WHIP and 73:27 K:BB across 51.1 innings while making 13 starts for the Bulls overall. He'll add depth to the Rays' staff down the stretch and will become the franchise-record 37th player on the active roster once he's officially activated.