By Judd Zulgad

CLEVELAND -- Tarvaris Jackson will be the No. 2 quarterback for the Vikings' regular-season opener at Cleveland on Sunday, according to people with knowledge of the situation.

This comes after coach Brad Childress refused to say this week whether Jackson or Sage Rosenfels would be the backup to starter Brett Favre. The move means that Rosenfels essentially will be inactive for the game.

NFL rules state that if the third quarterback plays before the fourth quarter, the first two quarterbacks cannot be used in the game at any position. "It's been a long time since that's happened [being the No. 3 quarterback]," Rosenfels said this week when discussing the possibility. "I've been at least a No. 2 for the last four years. That's a tough situation. You can never have too many good quarterbacks."

Rosenfels was acquired from Houston for a fourth-round pick last February and was expected to battle Jackson for the starting job in training camp. But that changed when Favre arrived after the first preseason game.

It remains to be seen if Jackson being the backup in Week 1 means he has won that job or if this will be a week-to-week situation. Childress did indicate that Jackson and Rosenfels could alternate as the No. 2 quarterback throughout the season depending on the opponent and how each guy practices during the week. Childress said he does not view it as a difficult situation because it's part of the process of determining which 45 players are active on game day.

The ability to play Jackson could be an indication the Vikings will put him on the field if and when they run their version of the Wildcast offense. That formation features wide receiver Percy Harvin at quarterback and calls for the QB to split out as a wide receiver. (At least so far). Favre did so twice in the three quarters he played against Houston and the second time the veteran threw a crack-back block on Houston safety Eugene Wilson that earned him a $10,000 fine. It also probably served as a caution to the Vikings that they don't want the soon-to-be 40-year-old Favre on the field when they lineup in the Wildcat.

The key with that formation is that opponents don't know what Harvin is going to do and the fact that Jackson is on the field would give defenses more to think about. Obviously, Favre is no real threat playing the receiver position.