An MRI revealed the injury to be a torn left ACL, Penn State announced Monday. Massaro, a starter in the Nittany Lions' final 11 games last season, will have surgery to repair the injury in the coming weeks and is expected to miss the entire 2011 season.
This is the second time Massaro has torn an ACL in the spring. He missed the entire 2009 season after injuring his right knee during the Blue-White Game that spring.
Massaro would have had junior eligibility in 2011.
Another starting defensive end, Jack Crawford, is sitting out spring drills after undergoing off-season surgery on a foot. He has been spotted at practice in street clothes wearing a protective boot.
But he is expected to be back at full strength in time for the 2011 campaign.