Asked if the Bills' pass rush would have had a different level of success had Adrian Peterson suited up for the Vikings in Friday night's preseason game, Vikings coach Leslie Frazier kind of smiled and said, "Well, I think every team that we play, they're going to have a plan for Adrian Peterson when you line up. So that's all I'll say about that."

That's one reason the Vikings aren't overly concerned about a first-team offense that's slogged through two preseason losses with only one drive that's lasted longer than three plays or gone farther than 15 yards. After all, it's tough to assess an offense built around Adrian Peterson when Adrian Peterson isn't around said offense.

That will change in the first half of Sunday's nationally televised preseason game against the reigning NFC champion 49ers in San Francisco. Frazier wouldn't say how long Peterson will play, other than he will not play into the early part of the third quarter, as most starters typically do in the third preseason game.

The Vikings also will game plan for the 49ers, something all teams typically do only for the third preseason game. So look for the Vikings to try to re-establish their run-oriented identity against the 49ers rather than continue experimenting with their passing game.

"Without Adrian Peterson in our scheme, it impacts our offense tremendously because he's the focal point," Frazier said. "Yeah, it definitely makes a difference. That will be obvious when we open up the season. It's obvious if you look at us from a season ago and it showed on Friday night [in a 20-16 loss at Buffalo].

"We didn't come into that ballgame saying we wanted to show Buffalo or anyone that we could be a dominant run team. We wanted to be able to do some things in the passing game. You saw us go up-tempo in what we call our red-ball offense. We were working on some things that we wanted to take a look at, and we'll do more of that this week as well. Our identity has not changed."

As for details of the plan for Peterson on Sunday night, Frazier would only say, "We have some set things in place that we want to see with him in the lineup. Not ready to divulge what those are right now. But we do have a plan for Adrian on Sunday night."

Ballard placed on active/left squad list

On the eighth day of his absence for personal reasons, defensive tackle Christian Ballard was placed on the active/left squad list. When or if he'll return is undetermined at this point.

"There is no timetable [for Ballard's return]," Frazier said. "We don't have to do anything at this point. Once we get to the 53[-man final roster], things change a little bit."

Frazier said he talked to Ballard before moving him onto the list, so Ballard's absence "is not without approval."

Although the Vikings have Kevin Williams and rookie Sharrif Floyd manning the under tackle position, Vikings defensive coordinator Alan Williams often preaches the importance of depth and rotation up front.

"[Ballard] is one of those guys we were counting on to be part of our rotation," Frazier said. "He did a very good job for us a season ago. We're hoping he'll be able to help us this year as well."

Kalil 'tweaks' knee

The Vikings returned to Winter Park for a short practice without pads Sunday afternoon. The most notable nonparticipant was left tackle Matt Kalil, who was nursing a sore knee.

"Don't worry," he said. "I'm fine. Just tweaked it a little in the game on Friday. I'll be fine."

Kalil is expected to return Wednesday when the team puts the pads on and starts preparing for the 49ers. The players are off Tuesday.

With Kalil out, backups Kevin Murphy and Brandon Keith took turns with the first unit.

Also missing practice Sunday because of minor injuries that shouldn't keep them out of Wednesday's padded practice were: Floyd, who tweaked the left knee he hurt in the Aug. 8 preseason opener, and long snapper Cullen Loeffler (elbow).

Wright running again

Wide receiver Jarius Wright (concussion) didn't practice, but he was running on the sideline, which is a good sign that he could be close to being cleared to return. Frazier has not ruled him out of Sunday's game.

Fullback Jerome Felton (appendectomy) watched practice Sunday. Frazier said the Pro Bowler is still on schedule to play in the Sept. 8 regular-season opener.