EDEN PRAIRIE, Minn. (AP) -- Mike Harris has been a major asset for Minnesota's offensive line.

His 6-foot-5, 340-pound frame is helpful, of course, but his versatility is really coming in handy for the Vikings.

Harris was a tackle in college at UCLA who lined up on different sides from snap to snap, so he came with experience at switching spots.

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When the Vikings claimed him off waivers last season from San Diego, Harris became the primary backup tackle and started the last five games on the right side after Phil Loadholt was hurt.

This season, there was an opening at right guard, and Harris was asked this summer to try it. The experiment, so far, has worked. Harris has been a steady presence on a front five in need of one.

"The coaches had trust in me and knew I could be a starting guy for them. Then I earned my position during camp," Harris said, adding: "It's just an honor and a privilege to start on an NFL team. I know there's a lot of responsibility involved, with preparation watching film, but this is my fourth year now. It's time to be a pro and go help this team win."

Proximity to the center, and thus the blocking calls made at the line in reaction to the defensive alignment, makes guard a more complex position than tackle. With right tackle T.J. Clemmings, Harris has also had a rookie relying on him for support.

There's still a lot for him to learn about his new spot, but he's had plenty of early success. Many of Adrian Peterson's 134 yards rushing last week in a victory over Detroit came behind Harris. With San Diego visiting Sunday, Harris will be even more motivated than usual to play a good game.

"The Chargers are a great team. I have all respect for them, but we're going to come ready," Harris said, smiling.

Center John Sullivan, of course, won't be ready. He's still recovering from back surgery. In his first interview since the herniated disc popped up in mid-August, Sullivan said he's hopeful but not certain of returning at midseason when he's eligible to come off injured reserve.

"People talk about iron man and all this stuff, but a huge measure of that is luck. If you get hurt, you can't play," Sullivan said. "It's been difficult to deal with at times, especially game days watching the team out there and feeling you should go through it with them. But it doesn't help you to get too emotional about it."

Sullivan has been predominantly walking to recover from the procedure done two weeks ago. Within the next two weeks, he'll be able to resume weightlifting.

"I understand it's completely illogical to feel guilty about being injured, especially in this sport, but you just can't help but feel you're letting people down," Sullivan said. "At times that's tough to deal with. I'm focused on what I can do to get back as fast as possible."