Mastrobuoni was optioned to Triple-A Iowa on Friday, Meghan Montemurro of the Chicago Tribune reports.
The move opens up a roster spot for Seiya Suzuki (oblique) to return from the injured list. Mastrobuoni slashed just .200/.200/.250 over 20 plate appearances during his time with Chicago, and he will likely remain in an organizational depth role while he's with Triple-A Iowa.