Horwitz is out of the lineup for Monday's game against the Brewers.
Horwitz batted leadoff in each of the last four games and got on base at a .389 clip while scoring two runs and driving in two more, but the Pirates haven't yet committed to using him regularly against left-handed pitching. With southpaw Jose Quintana on the hill for Milwaukee, the left-handed-hitting Horwitz will give way to the right-handed-hitting Liover Peguero at first base.