Lee is arguably the Cowboys best defender and someone they have missed heavily in the past few seasons.
The 26-year-old is rated as the fifth best inside linebacker in the NFL, but injuries have restricted him to the 25th position in the NFL in terms of time played amongst inside linebackers in the league.
This knee injury could prove to be very costly ahead of the new season, with first round draft pick Zach Martin playing his role in injuring Lee.
"Reviewed tape of Lee injury: started slipping and then 1st rounder Zach Martin engaged him & took him to ground."
It's clear that Martin unintentionally injured Lee in what could be most unfortunate of first OTA's for the rookie offensive guard.
Lee going down injured is the last thing that the Cowboys wanted to happen in their first OTA practice. We'll find out in time how bad Lee's injury is, with Cowboys personnel fearing he might be out for the whole of the 2014 season.
Watch this space.