Vikings need spark with Peterson out

As the Vikings head into Sunday's game against the Broncos, here are four questions we're trying to answer.

1. What will Adrian Peterson's absence mean to an already sputtering offense?

For all the warranted criticism the Vikings have taken, at least they're handling Peterson with care and not rushing him back. Coach Leslie Frazier has ruled Peterson out for Sunday, still not confident the star running back has recovered enough from a high ankle sprain to be ready for game action.

"The work he did [Friday] was far better than a week ago," Frazier said. "So he's able to do things straight-line pretty good. But the cutting is still a little bit of an issue."

With Peterson out, Toby Gerhart will get his second consecutive start, asked to revive a lifeless offense.

Since the bye week, the Vikings have started games in a somnambulant state, outscored 58-7 before halftime of their past three losses.

The team's first-half numbers since the bye: 17 possessions, 20 first downs, one touchdown, nine punts and an average of 22 yards per series.

2. What is the ripple effect of Donovan McNabb's exit?

The Vikings chose to fill McNabb's open roster spot by claiming Sage Rosenfels off waivers. Rosenfels, who was on Miami's reserve/non-football injury list before being waived Thursday, will spend the next month as the Vikings' No. 3 quarterback.

That's a familiar position for the 11th-year veteran, who was third on the depth chart behind Brett Favre and Tarvaris Jackson here in 2009. Now, he'll back up Christian Ponder and Joe Webb.

McNabb, meanwhile, went unclaimed on waivers after reportedly requesting his release earlier this week. That means the Vikings have to pay the remainder of his $5.05 million salary for 2011.

One last note: It will be interesting to see whether Rosenfels' arrival will give Frazier more comfort and more of an opportunity to use Webb as a wide receiver.

With Peterson out, Harvin might be the only dynamic offensive playmaker the Vikings have Sunday. As proof, he had a 39-yard touchdown catch and a 104-yard kickoff return in the fourth quarter last weekend in Atlanta. But the Vikings continue to face the challenge of using Harvin wisely as he deals with health issues. A rib injury has limited Harvin throughout this season. He also missed Friday's practice because of an illness and is listed as questionable for Sunday.

Asked how dire things would be if Harvin couldn't play against Denver, Frazier recoiled.

"Oh, man. Please, please, please, let's not go down that road," he said.

Even if Harvin plays as Frazier anticipates, he won't be used as often as most fans would like. That's just the way it is with Harvin.

Special teams coach Mike Priefer, for example, said this week he'd have Harvin returning every single kickoff if he wasn't needed for offense. As it stands, Harvin has 11 of the team's 36 kickoff returns this season, despite a 36.2-yard average.

"The pounding that he would take," Priefer said. "You're going to take some shots. You're not always going to hit that seam and go 104 yards. You'd hate to take a huge part of our offense out of the game for a quarter or two quarters or even the whole game, if he takes a shot to his ribs or the head."

4. What else is up on the injury front?

Guard Anthony Herrera should be back starting Sunday for the first time in six weeks. Frazier also anticipates tight end Kyle Rudolph -- questionable because of a quadriceps injury -- to play.

Others who are questionable for Sunday: cornerback Asher Allen and linebacker E.J. Henderson, both with shoulder issues.