The Dallas Cowboys fear that linebacker Sean Lee has torn the anterior cruciate ligament in his left knee, according to multiple reports.

Lee got hurt when he ran into rookie offensive lineman Zack Martin.

According to the Dallas Morning News, Lee's knee gave out prior to to Martin falling on him.

“I don’t really know what happened, two guys playing hard and running to the ball, so we’ll see what happens,” Martin said. “It sucks to see someone go down. It happens and I can only hope for the best.”

“We keep preaching, ‘Stay off the ground. Stay off the ground,’” Cowboys coach Jason Garrett said. “That’s a really important thing. Injuries happen when guys hit the ground.”

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Aaron Wilson covers the Ravens for The Baltimore Sun