While the quarterback's teammates practiced at Saracens Rugby Club's Allianz Park, Romo remained at the team hotel to get treatment on his back. Coach Jason Garrett said Romo, who sustained two small fractures in his back in a Week 8 loss to the Washington Redskins, did not have a setback. As part of his routine, and because of offseason back surgery, Romo hasn't practiced on a Wednesday since Week 2.
"It's just based on the feedback and based on what he's told us about how he feels," Garrett said. "Is it more worthwhile to stay there and get treatment or come here and watch practice and stand up for a couple hours? So it makes sense to stay back there, get some treatment."
Romo has taken part in two walkthroughs since the Cowboys arrived Tuesday morning in London, and he's been an active participant in meetings.
"Hopefully," Garrett said, "he'll be ready to go and do something (Thursday)."
Romo indicated to reporters on Tuesday that the flight from Dallas to London caused no issues.
"The flight was fine," said Romo, who is in his 12th NFL season. "I slept, it went by quick, and that part of it was no problem. It's progressing. Each day, it gets a little bit of improvement."
But Tuesday's walkthrough and "dynamic warmup" -- Garrett's words -- weren't exactly strenuous.
"If you couldn't go in the walkthrough," Romo said, "you'd probably struggle getting ready for practice."
What happens Thursday will go a long way toward determining Romo's availability going forward. A team source told NFL Media there is a strong likelihood Romo will practice Thursday. If he practices and does not have a setback, he is expected to start Sunday.
Schein: Do the right thing, Dallas
Weeden was 18 for 33 for 183 yards, one touchdown, two interceptions and a passer rating of 55.5 against Arizona. He took all of the first-team reps Wednesday.
Since Romo -- whose passer rating this season is 103.6 -- became the starter in 2006, the Cowboys are 69-47 with him and 6-9 without him. Also in that span, Dallas' offense has averaged 2.5 fewer points and 42.4 fewer yards per game without Romo, according to NFL Media research.
Yes, the Cowboys miss Romo when he's out. The question is, will they miss him again Sunday at Wembley? If Romo can't go, his absence will be felt team-wide.
"If we don't have Tony, each of us has to do a little more," cornerback Orlando Scandrick told NFL Media on Wednesday. "We just all have to do our job a little better."
From Jerry Jones to Garrett to Romo himself, there has been optimism that he will be able to play. Witten said he is "hopeful," but has to prepare for the possibility Romo won't be able to go.
"One thing you can't really question is the toughness and the will that (Romo) has, and he's shown it time and time again throughout his career," Witten said. "I know, right now, the way he prepares himself and the way he works, he's going to do everything he can to give himself a chance."