The Pirates are expected to place Horwitz (hamstring) on the 10-day injured list, Kevin Gorman of TribLive.com reports.
Horwitz was lifted from Wednesday's game against the Mariners because of left hamstring discomfort. It's unclear at this point how severe the strain is, but even a mild one could knock Horwitz out through the All-Star break. While Horwitz is sidelined, the Pirates will likely use Ryan O'Hearn at first base and Marcell Ozuna at designated hitter most days.