Sullivan, who underwent back surgery on Wednesday, has been placed on IR/designated to return by the Vikings, the Minneapolis Star-Tribune reports.

Under the rules of IR/designated to return, Sullivan will miss at least eight games, with Joe Berger now in line to serve as the Vikings' starting center in the meantime.

Sullivan agreed to a contract extension that will pay him $5.4 million in each of the 2016 and 2017 seasons, the Minneapolis Star Tribune reports.

He'll return as Minnesota's starting center and anchor on the offensive line. He started all 16 games for a third consecutive seasons.

Sullivan cleared the NFL's concussion protocol and is in line to play Sunday, ESPN reports.

Sullivan left last week's game after suffering a concussion, but it looks like he won't miss a game. He was a limited participant in Thursday's practice.

Sullivan suffered a concussion in Sunday's loss at Buffalo, the Minneapolis Star Tribune reports.

The Vikings may have depth issues on the offensive line as right guard Vlad Ducasse suffered a knee injury as well.

Vikings C John Sullivan (concussion) has been fully cleared for Week 12.

He passed all of his concussion tests and will start against the Packers.

Vikings C John Sullivan suffered a concussion in Sunday's Week 11 loss to the Seahawks.

His status is uncertain for Week 12 against Green Bay, but the Vikings really need him against B.J. Raji & Co. Sullivan has graded out as a top-11 center in Pro Football Focus' 2013 ratings. He finished last season No. 1 overall.

Vikings C John Sullivan (microfracture surgery) is full go for training camp.

Vikings C John Sullivan (microfracture surgery) is on track to be ready for the start of training camp.

Sullivan said he was "on target to start when we start, so hopefully, that'll still be the case" after the team wrapped up its final minicamp practice Thursday. The former Golden Domer underwent microfracture surgery shortly after the season ended. Sullivan graded out as Pro Football Focus' No. 1 center in 2012.

Vikings center John Sullivan (microfracture surgery) continues to progress from offseason surgery.

Coach Leslie Frazier says his standout center is on track in his recovery, but added the team "still has to see a little more progress." Frazier intimated that everything is fine physically, but he'd like to see Sullivan "continue to gain confidence and not be worried about the surgery." It sounds like Sullivan's biggest challenge will be with the mental aspect of coming off an injury. He's expected to be medically cleared for the start of camp.

Vikings C John Sullivan (microfracture surgery) expects to be ready for training camp.

Sullivan says his rehab has "progressed smoothly," and that he's confident his play will not drop off after being one of the league's top centers in 2012. Sullivan was a big part of the reason why Adrian Peterson came within eight yards of the single-season rushing record. Microfracture operations - even supposedly minor ones like Sullivan's - are extremely tricky to recover from, so Sullivan shouldn't be considered out of the woods until he's back on the field in preseason action.

Two NFL sources tell ESPN 1500 Twin Cities Vikings C John Sullivan underwent microfracture surgery on his left knee last week.

Vikings signed C John Sullivan to a five-year, $25 million contract extension.

ESPN 1500 Twin Cities' Tom Pelissero reports the deal includes $10 million guaranteed. It's an impressive haul for a player who mostly struggled during his first three years in the league before turning the corner this season. Sullivan has graded out as Pro Football Focus' second best center through the season's first 14 weeks.

The Vikings have reportedly approached neither C John Sullivan nor OLB Erin Henderson about a contract extension

Both players are due to hit free agency in 2012. Pushed around in his first two seasons as a starter, Sullivan has surprisingly graded out as Pro Football Focus' third-best center this year. Henderson has excelled in run defense as a first-year starter. Still in their mid-twenties, both players would seem to be candidates for long-term deals.

Vikings C John Sullivan left Sunday's game with a concussion and did not return.

He will undergo NFL-mandated testing to determine his status for Week 7, and backup Joe Berger has replaced him tonight. RT Phil Loadholt (knee) has also left the game and is questionable to return. Pat Brown has replaced Loadholt, as the Vikings' line is crumbling amidst a 33-10 route mid-way through the third quarter.

Vikings C John Sullivan is expected to face competition for his starting job in training camp.

The Vikes see something in Sullivan, but he's shown a severe lack of power at center. Sullivan has graded out as one of the least effective starters in the league in each of the past two seasons, according to Pro Football Focus.

Vikings C John Sullivan doesn't think the aggravation of his calf injury is as serious as when he first suffered the malady.

Sullivan aggravated the injury on the Vikings' first offensive series and sat out the remainder of the game. The initial injury cost him two games, but it remains to be seen if he'll be able to play in Week 11. Jon Cooper will play if Sullivan isn't ready and isn't a noticeable downgrade.

Vikings C John Sullivan left Sunday's game against the Bears in the first quarter with an apparent leg injury.

Sullivan has been dealing with calf issues all season. Jon Cooper is coming in.

Vikings coach Brad Childress said Vikings C John Sullivan (calf) will likely return to the starting lineup Sunday after missing the last two games.

Chilly did add that Jon Cooper, who started the last two games, could play a series or two depending on Sullivan's stamina. Sullivan isn't much of an upgrade over his backup.

Vikings C John Sullivan (calf) was unable to practice Monday.

He's had the calf issue for a few weeks now and his status for Week 5 is seriously in question. It wouldn't be much of a loss to not have him, as Sullivan often gets bullied by opposing defensive tackles. Jon Cooper is the backup center.

John Sullivan left Sunday's game in the first quarter with a leg injury.

Sullivan isn't exactly a big loss given how he played through two weeks, but Minnesota's backup center, Jon Cooper, is inactive. Ryan Cook is in at center.