The newspaper reports Roy was medically cleared prior to the trade with the Buffalo Sabres that included Steve Ott but the problem was discovered during a more intense physical in Dallas. Specifics of the injury were not disclosed.
"He played through it before and he could have played through it again, but we want the best Derek Roy we can get," Nieuwendyk told reporter Mike Heika. "It was a group decision, and we felt [surgery] was the best decision."
Roy was acquired by Dallas on July 2 in exchange for Ott and Adam Pardy. Roy had 17 goals and 27 assists in 80 games last season.
On Tuesday, Nieuwendyk said the team did not expect to trade captain and forward Brenden Morrow despite rumors of interested teams.