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. Eagles coach Andy Reid said Vick would remain Philadelphia's starting quarterback if healthy but acknowledged that the four-time Pro Bowler still must undergo tests.
"I was hoping he'd make it through without having a concussion, but that's where we sit right now with him," Reid said.
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.
"Not good enough to win," Foles said. "I made some mistakes and I can't turn the ball over. That's the most important thing to win games."
With a 3-6 record, it might be too late for the Eagles, no matter who the quarterback is, to save their season.
Reid said Foles did a good job.
"He kept battling, he kept his eyes downfield," Reid said. "There were some positives."
Vick looked like his old self on the first drive of the game, completing passes for 17 and 31 yards, before connecting with Riley Cooper for a 2-yard TD pass. Cooper made a sensational one-handed grab on a fade route and gave the Eagles their first points on their first drive of a game all season.
Vick has been under relentless pressure all season, in part due to the fact that the Eagles are missing four starting offensive linemen.
ESPN.com's Dan Graziano and The Associated Press contributed to this report.