The Cowboys have been here before.

Sean Lee never has played a full season, missing 18 games in his career. A strained hamstring and a sprained neck kept him out of five games last season, with the Cowboys starting three players at middle linebacker in Lee’s absences. Ernie Sims, Justin Durant and DeVonte Holloman all filled in for Lee at various times last year.

The Cowboys expect to be without Lee for all of 2014 after their defensive leader and middle linebacker tore the anterior cruciate ligament in his left knee, according to sources.

“Obviously, it’s a huge loss to our team, especially our defense, but at the same time, guys have to step up,” weakside linebacker Bruce Carter said. “It’s kind of bad to say, but we’ve been in this situation before. Guys have got to step up and just play their role.”

Safety Barry Church and cornerback Brandon Carr expect to fill Lee’s leadership role, but Carr said all 11 players need to contribute.