Cowboys linebacker Dan Connor did not return after halftime of Sunday's game against the New York Giants because of a neck strain.
The Giants also lost a starting linebacker when Chase Blackburn was knocked out of the game in the second half because of a left hamstring injury.
Connor, who started in place of injured leading tackler Sean Lee, got hurt early in the second quarter. He remained down on the ground at the end of a play when the Giants fumbled.
The Cowboys said Connor was out of the game.
Lee was put on injured reserve this week because of a big toe injury sustained in last week's win at Carolina that will require season-ending surgery. Lee was on the sideline in crutches Sunday.
Giants tight end Bear Pascoe had X-rays on a sprained ankle and the team said his return was doubtful.