Hjelle (leg) was injured in Thursday's game versus Double-A Somerset.
Hjelle appeared to injure his leg on a pitch in the first inning. The 24-year-old has posted a 3.48 ERA, 1.30 WHIP and 42:10 K:BB across 33.2 innings in eight starts this year. He's added a 3-1 record. It's unclear when he'll be able to return to action.