Wales centre Tyler Morgan will require surgery on his shoulder but should recover in time to be fit for the Six Nations.
Morgan dislocated his shoulder in Saturday's quarter-final loss to South Africa and joins fellow Newport Gwent Dragons Hallam Amos and Jack Dixon on the sidelines for the rest of 2015.
Dragons director of rugby Lyn Jones admits it's a real blow to the team, with all three young backs out for an extended period.
"It's devastating news," Jones told the South Wales Argus.
"When I saw Tyler walking around with his arm in a sling on Saturday I feared the worst and that is the case.
"It's really, really difficult to deal with. As a coach you have to deal with negatives all the time and turn them into positives but with us it's one thing after another with injuries.
"We just have to soldier on and do our best. We are trying to develop a team for the future here and we've been investing a lot of time in the young players, but they need to be on the field for us.
"They are three key players who are out long term."