PHILADELPHIA (CBS) — Tuesday was the beginning of off-season team activities (OTA’s) for 25 NFL teams, with the others beginning on Wednesday.

Cowboys linebacker, Sean Lee, suffered an injury on day one of the OTA’s that is reportedly season-ending.

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NFL insider Ian Rapoport reported on Tuesday night that Cowboys linebacker Sean Lee has a torn ACL and is expected to miss the 2014 season, according to a source.

According to 105.3 The Fan in Dallas, Lee collided with rookie offensive lineman Zack Martin and appeared to have injured his “lower leg”.

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Lee suffered major injuries to both of his knees during his final two years at Penn State, has also battled through injuries in his four years with the Cowboys.

After missing time in 2012 with a toe injury, Lee appeared in just 11 games for the Cowboys in 2013 due to a torn ligament in his neck.

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