How much could Adrian Peterson help Vikings?

Adrian Peterson was spotted running on the side at Tuesday's practice, marking the first time he has run in front of reporters since his Sept. 22 knee surgery.

It was the media's first look at Peterson, but the quick-healing running back had already resumed sprinting, according to coach Mike Zimmer, who said he didn't know exactly when because "I'm not in charge of the rehab."

"He's doing good. He's doing good," Zimmer said. "He's probably ahead of schedule, I guess. I don't know."

Peterson, 31, is eligible to be brought off injured reserve, although his return does not appear imminent since he still has yet to practice.

Peterson underwent a full surgical repair days after suffering a lateral meniscus tear in his right knee during a Week 2 win against the Packers. The future Hall of Famer certainly would help a Vikings running game that is on pace to be one of the NFL's all-time worst. However, on 31 carries, Peterson only averaged 1.9 yards per carry before the injury.

"I know when he makes the decision to come back, he's going to be ready to go," running back Jerick McKinnon said. "He's one of the captains on this team, so anytime you see him fighting, pushing and just working hard, it motivates you on the inside to do better."

During a week when quarterback Sam Bradford called for more "explosive plays," Peterson's presence outside of the athletic trainer's room is a sliver of hope for their lackluster offense.

Second-year center Nick Easton is in line to make his first NFL start Thursday against the Cowboys after Joe Berger was unable to practice Sunday through Tuesday because of a concussion.

"He played very well last week," Zimmer said of Easton. "We expect the same this week."

Easton's first start would mark the Vikings' sixth different offensive line combination through 12 games. Easton, who played at Harvard, has played 33 snaps this season, most while spelling Berger during last week's loss in Detroit. The Vikings acquired Easton a year ago during the trade that sent linebacker Gerald Hodges to San Francisco.

"Nick's been doing a great job in there," Boone said. "Sometimes I get upset because he's from Harvard, so he's very literal with everything. You try to joke with him a little bit and he doesn't laugh; drives me nuts."

Three Vikings defensive backs took a step forward in practice Tuesday as cornerback Terence Newman (neck) was upgraded to a full go and cornerback Captain Munnerlyn and safety Harrison Smith made their limited returns.

Bradford was limited again during Tuesday's practice because of an ankle injury. Defensive end Everson Griffen was a midweek addition to the injury report. He was limited Tuesday because of a shoulder problem.

The Greenway family welcomed their fourth child — another baby girl — into the world on Monday afternoon. Linebacker Chad Greenway had said there was a chance he'd miss last week's game in Detroit if the baby came, but she waited until he returned.

"So I didn't get much sleep last night, that's kind of how it goes," Greenway said. "Everybody is happy and healthy."

Greenway returned to practice Tuesday and is expected to play Thursday against Dallas.