Manager Dave Martinez said Wednesday that Hassell has been diagnosed with a strained groin, Andrew Golden of The Washington Post reports.
Hassell suffered the injury during a Grapefruit League game last week. He's not been shut down and will still able to do some baseball activities, but Hassell isn't scheduled to play in any games for a while. Once healthy, the 22-year-old is likely to begin the season at Double-A Harrisburg.