Rookie quarterback Matt Barkley replaced Foles in the fourth quarter.
Foles, starting his second game in place of the injured Michael Vick, was sandwiched between Cowboys defenders George Selvie and Jarius Wynn on the final play of the third quarter. He was slow to get up and, after being examined by medical staff on the sideline, left the field for an evaluation.
Foles, 24, was named NFC Offensive Player of the Week for his performance against Tampa Bay last Sunday. That had speculation running high that Foles could retain the starting job when Vick recovered from his hamstring injury.
But Foles struggled badly against the Cowboys before the injury. He completed 11-of-29 passes for 80 yards and took three sacks.
Barkley struggled in his NFL debut, completing 11-of-20 passes for 129 yards while throwing three interceptions.
"I was maybe a little too aggressive on some of those throws, trying to advance the ball down the field and help our team win," Barkley said. "I learned a lot today. I'll learn even more watching the tape."