The Cubs optioned Roberts to Triple-A Iowa on Tuesday, Meghan Montemurro of the Chicago Tribune reports.
The move is to make room on the 26-man roster for Mark Leiter (forearm), who was reinstated from the 15-day injured list. Roberts made three appearances out of the Cubs' bullpen since being called up from Iowa on June 28, allowing five hits and two walks while striking out three over four scoreless innings. Roberts hasn't allowed an earned run over 13.1 innings in Triple-A this season, and the 27-year-old right-hander should be in line for another call-up this season should the Cubs need help out of their bullpen.