Graves is dealing with a left oblique strain, Clark Spencer of the Miami Herald reports.
Graves suffered the injury during Tuesday's Grapefruit League contest against the Cardinals, exiting with a trainer in the first inning after recording just two outs. The Marlins have yet to announce a possible timetable for Graves' return, but oblique injuries tend to linger, and depending on the severity of the issue, the Rule 5 pick could very well be sidelined beyond Opening Day. Look for a more concrete timetable to emerge in the coming days, once he's further evaluated.