Vick was knocked on his back in the second quarter by linebacker Ernie Sims on an incomplete pass and was slow to get up. He headed for the locker room and rookie Nick Foles started warming up. Vick, however, may have been injured on the previous play when he was driven from behind head-first into the ground by tackle Jay Ratliff.
Vick did not talk to reporters but appeared groggy in the locker room.
Foles received a big ovation when he took over with the game tied 7-7 in the second quarter. Foles was a third-round draft pick out of Arizona and had a strong preseason for the Eagles.
Foles was 22 of 32 for 209 yards and one touchdown. He had an interception returned by cornerback Brandon Carr 47 yards for a touchdown that put the Cowboys up 31-17.
With a 3-6 record, it might be too late for the Eagles, no matter who the quarterback is, to save their season.
Coach Andy Reid said he'd determine the starter for Sunday's game at Washington based on Vick's health. He said Foles did a good job.
"He kept battling, he kept his eyes downfield," Reid said. "There were some positives."
Vick threw a 2-yard touchdown pass to Riley Cooper in the first quarter.