Graterol was placed on the 10-day injured list with right forearm tightness Thursday, Juan Toribio of MLB.com reports.
Graterol has been used sparingly after a delayed start to the season, as he's thrown only 1.1 innings across three appearances. It's unclear when he suffered the injury, though he last pitched April 26. The nature of the injury is cause for some concern, but no timeline for his absence has been disclosed.