Mastroianni was placed on the 15-day disabled list Wednesday with a left oblique injury, Rhett Bollinger of MLB.com reports.
Mastroianni logged nine at-bats in seven appearances in the majors this season before injuring his oblique, recording two walks, zero hits and four strikeouts. Mastroianni provided direly needed outfield depth for the Twins, but it's not a lock that he'll have a 25-man spot waiting for him once healthy.