The Cubs optioned Mastrobuoni to Triple-A Iowa on Tuesday, Andy Martinez of Marquee Sports Network reports.
With the selection of Jared Young from Triple-A on Tuesday, Mastrobuoni will head back to the minors to make room for the promising prospect. Mastrobuoni holds an impressive .949 OPS in Iowa this season, but has yet to put it together in Chicago, where that figure sits at just .431.