Romo suffered two transverse process fractures in last week's loss to the Washington Redskins, according to sources. While there can be no further damage, Romo did not practice all week and remained in a good amount of pain later in the week.
Weeden threw two interceptions as the Cowboys (6-3) dropped their second straight after a six-game winning streak, losing 28-17.
The Cowboys leave for London on Monday to get ready for their Nov. 9 meeting against the Jacksonville Jaguars at Wembley Stadium. After the game on Sunday, Romo said he will travel to London and prepare as if he's playing.
Cowboys coach Jason Garrett said he is hopeful Romo will be able to play next week. Cowboys owner Jerry Jones would not make any guarantees, but did say he is "betting on it."
Romo took a knee to the back in the third quarter of the loss to Washington. He was able to return to the game for the Cowboys' final two drives after X rays at the stadium were negative. He had a CT scan the day after the game.
The Cowboys and Romo stressed that this injury is not related to the disk surgery he had last December.
Weeden took all of the first-team snaps this week and will make the 21st start of his career. He went 5-15 in two years with the Cleveland Browns. In Romo's absence Monday, he completed 4-of-6 passes for 69 yards and a 25-yard touchdown to Jason Witten.
"I think the thing that was most important was [Weeden's] demeanor," passing game coordinator Scott Linehan said last Thursday. "He looked very veteran-like. You could tell he'd played. You know, he's an older player. Young in the league, but the guy's got a lot of maturity to him. It's not too big for him to go out there and step in in a relief mode and play, nor is it too big for him to be prepared as a starter because he's done it in this league. We're very confident in him."
With Romo sitting out most Wednesday practices this year, Weeden has taken plenty of snaps with the first-team offense during the season, which is not normal for backup quarterbacks. He also took the snaps in the organized team activities, mini-camp and every third day of training camp with Romo rehabilitation from back surgery.
ESPN's Ed Werder contributed to this report.