ESPN is reporting that Dallas Cowboys linebacker, Sean Lee, was helped off the practice field Tuesday (May 27th) with an apparent knee injury.

According to ESPN Dallas, Lee was up against the Cowboys' first round draft pick, Zach Martin, when he slipped and injured his knee. The Cowboys have not made an official statement, but ESPN's Ed Werder is reporting that Lee has been told he has torn his left ACL and will be out for the season.

Lee has been plagued with injuries, missing 5 games last year because of an injured hamstring and neck. In 2012, he missed 10 games because of a bad toe.

If Lee's injury is that serious, this would be a huge blow to a Cowboys defense that was ranked last in 2013.