The Cubs optioned Roberts to Triple-A Iowa on Saturday, Jared Wyllys of AllCHGO.com reports.
Roberts owns an impressive 1.96 ERA and 1.09 WHIP through 18.1 innings on the year, but he's given up four runs (three earned) over his last three outings and will now return to Triple-A to get back on track. Javier Assad was recalled from Iowa to fill the open bullpen spot.