O'Hearn is out of the lineup for Sunday's Grapefruit League game against the Red Sox due to a sore knee, Andy Kostka of The Baltimore Sun reports.
O'Hearn recently suffered the injury while making a leaping play in the outfield, and he's currently considered day-to-day. The 29-year-old is a longshot for the Opening Day roster after being outrighted off Baltimore's 40-man roster in January, and any prolonged absence will only further reduce his chances of making the team.