NFL Media's Albert Breer reports that Lee did not suffer a multi-ligament tear, per a Cowboys source. With the injury only to his ACL, it cuts down the recovery time.
It's a devastating blow for Lee, who has missed 15 games over the last two seasons due to wrist, neck and hamstring problems. When he's fully healthy, Lee mixes great run pursuit with rangy pass coverage as well as any linebacker in the league. He was expected to anchor a Cowboys defense that looks particularly soft up the middle with holes at defensive tackle and questions next to Lee at linebacker.

http://www.nfl.com/news/story/0ap200...s-cowboys-otas

Over before it started tough break for Lee.