The Cubs optioned Assad to Triple-A Iowa on Sunday, Jesse Rogers of ESPN.com reports.
Assad lost his spot in the rotation in the aftermath of the Aug. 3 trade deadline, and after making his last two appearances as a reliever, he'll now end up losing his spot on the active roster after the Cubs reinstated Edward Cabrera (hamstring) from the 15-day injured list ahead of his scheduled start versus the Cardinals. Even though the Cubs now have a full rotation, Assad is expected to get stretched back out at Triple-A to offer insurance in case injuries test the big club's starting depth down the stretch.