The Pirates placed Hernandez on the 15-day injured list Sunday with a right calf strain, Jason Mackey of the Pittsburgh Post-Gazette reports.
Hernandez was a Rule 5 draft selection by the Pirates over the winter, and the left-hander has more than held his own with a 2.63 ERA and 1.02 WHIP over 26 appearances and 27.1 innings with the club. He'll be out for at least the next two weeks, however, and Ryan Borucki was recalled from Triple-A Indianapolis in the corresponding transaction.