Mastrobuoni is out of the lineup for Wednesday's game against the Orioles.
The lefty-hitting Mastrobuoni had been included in the lineup in each of the Cubs' last three matchups with right-handed pitchers, but the uptick in playing time looks to have been the result of outfielder Pete Crow-Armstrong being unavailable due to a thumb injury. After serving as a pinch runner in Tuesday's 9-2 win, Crow-Armstrong has received the green light to re-enter the starting nine Wednesday for the first time in a week, so Mastrobuoni will head back to the bench.