Dallas Cowboys cornerback Morris Claiborne tore his anterior cruciate ligament in his left knee, according to owner Jerry Jones.
A magnetic resonance imaging exam will confirm the initial diagnosis.
"We'll get more on it, but it doesn't look good right now," Jones said. "I hope we've got a big surprise for us in the morning."
Earlier in the week, Claiborne skipped practice when he was told he wouldn't start. He later apologized.
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Aaron Wilson covers the Ravens for The Baltimore Sun