"We don't know how long he'll be out ... it depends on how fast that heals," said coach Wade Phillips, who says there won't be any surgery. "I'd say week to week, depending on quickly he heals. Different people heal differently."
The injury leaves the Cowboys (4-2) with 40-year-old Brad Johnson as the starter for Sunday's game at St. Louis. Johnson, who won a Super Bowl with Tampa Bay, hasn't started a game since 2006 in Minnesota.
Neither Romo nor Johnson was in the locker room Monday when it was open to reporters.
When linebacker Greg Ellis was told about Romo's broken finger, he got a somewhat stunned looked on his face and exclaimed, "Wow!" Bradie James said the players will have to rally around each other.
"We've got to play relentless football now without our signal caller, our leader, our captain on the offensive side," James said. "That's the thing about a season; you never know what can happen. You hope you are playing some real good ball when things go down, so here we are and now we've got to make some adjustments and move on."
Receiver Terrell Owens refused comment, getting agitated when he saw cameras recording him. "Today is not Wednesday," he said, referring to the day he routinely talks to reporters.
On Sunday, Romo missed on three straight passes to start the overtime, after passing for 321 yards and three touchdowns despite heavy pressure. He was sacked three times and knocked down 19 times.
"Obviously, he had trouble throwing the ball that last series in overtime," Phillips said.
Romo, whose hand was heavily wrapped after the game, fumbled three times Sunday, losing one, but didn't throw an interception for the first time in the last nine games.
Through Sunday's games, Romo ranks second in NFC passing with a 103.5 rating. He has thrown for 14 touchdowns and been intercepted five times. He had his team-record 14th career 300-yard passing game Sunday in his 32nd start. That broke a tie with Troy Aikman, whose 13 were accomplished in 165 starts.
In 2007, his first full season as a starter, Romo led the Cowboys to a 13-3 record, best in the NFC. He set team records with 335 completions for 4,211 yards and 36 touchdowns, including the team-record 15 receiving by Owens, in a season that ended with a loss to the Giants in the playoffs.
It was two years ago this month that Romo replaced Drew Bledsoe as the starter.
Johnson quarterbacked the Tampa Bay Buccaneers to the NFL championship in 2002, and is the only member of the Cowboys with a Super Bowl championship ring. He has been Romo's backup since last season and threw only 11 passes in 2007.
Johnson, in his second year as Cowboys backup, has only seen brief mopup duty in Dallas, going 7-for-11 for 79 yards. Before coming to Dallas, Johnson started 122 of his 145 career games with Minnesota (1993-98, 2005-06), Washington (1999-2000) and Tampa Bay (2001-04).
Johnson has completed 2,627 of 4,248 career passes (61.8 percent) for 28,627 yards with 164 touchdowns and 117 interceptions. He passed for 2,750 yards in 2006 with nine TDs and 15 interceptions - only the third time in his career with more interceptions than TDs.
"It's going to be Brad to go in there and prove that he's not just here for the ride, he's part of this thing," Ellis said.
"Every opportunity I've seen Brad step in on other teams, he's able to hold it down and get it done."
Another former Viking, Brooks Bollinger, will be Johnson's backup. The team doesn't plan to bring in any other quarterbacks, Phillips said.
The Cowboys also sustained other injuries Sunday.
Rookie running back Felix Jones strained his hamstring and was having and MRI on Monday. Punter Mat McBriar, who was carted off the field after his kick was blocked on the game's final play, also was having an MRI. The team doesn't know the extent of his injury yet, Phillips said.
