Dallas Cowboys linebacker Sean Lee was helped off the field, according to Dallas reporters.
Lee was knocked down by rookie first-round offensive lineman Zack Martin.
Lee has a history of injuries and has yet to play a full season.
Lee is one of the best linebackers in the NFL when he's healthy.
He was signed to a seven-year, $42.6 million contract last year.
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Aaron Wilson covers the Ravens for The Baltimore Sun
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