Coach Jason Garrett said Romo had back surgery Friday, and Kyle Orton will start when Dallas faces Philadelphia on Sunday night with the NFC East title and a playoff berth on the line.
Garrett said Romo underwent treatment all week in hopes of playing after injuring his back in a season-saving 24-23 victory against Washington. The winning touchdown came after the injury on Romo's fourth-down pass to DeMarco Murray in the final 2 minutes.
Romo injured himself when he tripped over his foot while trying to escape pressure earlier in the fourth quarter.
"He might have had his finest hour against the Redskins last week, what he did at the end of that ballgame under the circumstances," Garrett said. "Pretty special."
Romo lost the past two winner-take-all finales - to the New York Giants two years ago and Washington last season. He also lost to the Eagles in the same situation in 2008.
Philadelphia (9-6) is trying to complete a worst-to-first turnaround from a 4-12 season under first-year coach Chip Kelly. The Cowboys (8-7) want to end a three-year playoff drought a third 8-8 finish in Garrett's three full seasons as coach.
Cowboys owner Jerry Jones said on his radio show that the team and Romo hoped an injection would ease the pain enough to allow him to play. But his condition didn't improve, and Jones said doctors advised it was better not to wait for surgery.
Jones said the hope is that Romo will be ready for offseason practices in May.
Romo missed all the offseason workouts this year after surgery to remove a cyst from his back in April. Garrett and Jones said the latest injury is not related, but wouldn't be more specific about Friday's procedure.
"From everything I know from talking to several people personally, there's no relation between these and wouldn't look to be ... of the chronic nature," Jones said.
Orton will make his first start since the finale in 2011, when he finished the season in Kansas City after getting replaced by Tim Tebow in Denver. He's appeared in three games and thrown just 15 passes in two seasons as Romo's backup.
"We've been operating as if Kyle Orton is going to be our starting quarterback," Garrett said. "At the same time we were trying to do whatever we could to see if we could help Tony and get him back as quickly as possible. We just felt like this was the best course of action."