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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AUG 28 Joel Corry
Between injuries, trades and positional battles, the financial landscape for several key players has shifted dramatically.
AUG 26 Joel Corry
The highly productive Dallas wideout is headed for a big-time payday.
AUG 22 Ari Nissim
Ten players closing in on lucrative new paydays.