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This is yet another setback for Lee, who has dealt with injuries throughout his career. A hamstring issue kept him out for three games earlier this season.
He played 11 games in 2013 and 2017, missed 2014 with a torn ACL and played just six contests in 2012.
In fact, the 32-year-old hasn’t played a 16-game slate in his entire career despite being in the league since 2010.
The two-time Pro Bowler did play a career-high 15 games in 2016 and earned First Team All-Pro recognition with 145 combined tackles. He has 27 combined tackles in five games in 2018.
While Lee is one of the leaders of the Cowboys defense, they do have other pieces to fill in at linebacker. The combination of Jaylon Smith, Leighton Vander Esch and Damien Wilson will likely see more time as Dallas tries to turn things around after a 3-5 start.