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.

‘‘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.