How do you assess an offense built around Adrian Peterson when Adrian Peterson isn't around said offense?

That's been one of the difficulties for the Vikings as they've sludged through two preseason losses with the reigning league MVP being rested and preserved on the sideline. That, however, will change on Sunday night when Peterson makes his first preseason appearance since 2011 when the Vikings play at San Francisco in a nationally-televised game.

"Yeah, it definitely makes a difference [not having Peterson]," coach Leslie Frazier said Sunday after a short non-padded practice at Winter Park. "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 [a 20-16 loss at Buffalo]."

The first-team offense, sans Peterson, has executed six drives in two games. Only one has lasted longer than three plays or gone farther than 15 yards.

The Vikings aren't panicked, however, because they haven't had Peterson and they've yet to game plan for an opponent. With Sunday night's game being the third preseason game, theVikings will game plan and play most of the starters into the early part of the third quarter.

Frazier said Peterson will not play into the third quarter. The coach said there's a plan being formulated for Peterson, but he's not ready to divulge that info just yet. Peterson didn't play in the preseason last year as he recovered from ACL surgery on his left knee. Rumor has it he did OK, running for 2,097 yards without preseason action.

The Vikings, however, are anxious to get their offense on track. And it's hard to right an offense built around Peterson when Peterson isn't around.

In other news:

. Defensive tackle Christian Ballard, who has been absent for personal reasons the past eight days, was placed on the active/left squad list. Frazier said the Vikings won't have to make a decision on Ballard's status until it's time to make the final roster decisions.

. Left tackle Matt Kalil missed Sunday's practice because of a knee injury. He said he "just tweaked it" and will be fine when the Vikings put the pads back on Wednesday.

. Also missing practice on Sunday were: DT Sharrif Floyd (knee), WR Jarius Wright (concussion) and LS Cullen Loeffler (elbow). None of the injuries are serious. Frazier said Wright might even play on Sunday.

. Frazier said FB Jerome Felton, who had an appendectomy on Wednesday, is on schedule to play in the Sept. 8 regular-season opener. Felton watched practice on Sunday.