IRVING, Texas — Dallas Cowboys quarterback Tony Romo has a broken finger on his throwing hand and could be out for up to four weeks.

Romo broke his right pinkie on the first play of overtime in a 30-24 loss at Arizona on Sunday, according to a posting on the team's official Web site. A team spokesman didn't immediately return a call seeking comment Monday.

The injury leaves the Cowboys (4-2) with 40-year-old Brad Johnson as the starter. Johnson, who won a Super Bowl with Tampa Bay, hasn't started a game since 2006 in Minnesota.

Romo missed on three straight passes to start the overtime, but before then passed for 321 yards and three touchdowns despite heavy pressure. He was sacked three times and knocked down 19 times.

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 Terrell 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. 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.

Another former Viking, Brooks Bollinger, will be Johnson's backup.