Three weeks ago, the Minnesota Vikings were unbeaten and appeared to be the class of the NFC.

Minnesota hosts the Detroit Lions on Sunday looking to just stay on top of the NFC North, and will do so with a new offensive coordinator.

The past two weeks, in which the Vikings (5-2) scored 20 total points and averaged 270 yards of offense in two losses, has taken the shine off Minnesota coach Mike Zimmer's Super Bowl-hopeful bunch.

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As the Vikings were getting set to prepare for Detroit (4-4), Vikings offensive coordinator Norv Turner resigned on Monday. Zimmer said he was "very, very surprised" by the move.

"He has helped me tremendously in the three years that I've been here," Zimmer said. "He has had an unbelievable career. He has been, really, my right-hand man, really, since I've been here, and he decided it was in the best interest of him to do this, and I accept the reasons; and they are personal."

Behind a faltering offensive line, the Vikings have the league's second-worst offense. Minnesota is 31st in the NFL in average yards per game (293.3) and yards per play (4.6). The offense has averaged 19.9 points per game, tied for 23rd in the league.

Tight ends coach Pat Shurmur is the interim offensive coordinator and will call the plays. Shurmur does have experience with quarterback Sam Bradford, who came to the Vikings in a trade right before the regular season began. Shurmur was the offensive coordinator and interim head coach in Philadelphia last year with Bradford, and the two were together in St. Louis as well.

"I think he's a great football mind," Bradford said. "Really just looking forward to sitting down and talking to him and trying to figure out the direction in which we're going to go...Halfway through the season, I'm not really sure if you can completely change an offense and the terminology for everyone."

Offense hadn't been a concern for the Lions, at least until Sunday's loss at Houston. Detroit had 289 yards of offense, its second-lowest output of the season in a 20-13 loss. The 13 points were a season low even as the Lions welcomed back tight end Eric Ebron and running back Theo Riddick.

Ebron returned after missing three games with ankle and knee injuries and had seven catches for a team-high 79 yards receiving. Riddick had missed two games with an ankle injury and had 56 yards rushing and 77 yards receiving with a touchdown against Houston.

"We just hurt ourselves," Ebron told the team's website. "Penalties, we just hurt ourselves. Every game we've lost, we've hurt ourselves. So, we've got to, just got to clean up our act and win."

Protecting Matthew Stafford will be an important factor against Minnesota's second-ranked defense. Stafford was sacked eight times in two losses to the Vikings last season.

"That's what they're known for, it's what they're really good at," Stafford told the team's website of the Vikings' blitz packages. "The last two times we played these guys we were a little different schematically than we are now.

"We'll be able to take a look at them this week, study them hard and work to try and find solutions that will fit us."

Detroit will also need to bring the pressure against Bradford, who has been sacked 11 times the past two weeks.

"It's something that I would like to see go down," Bradford said of the number of times he has been hit. "I don't think it's a positive thing. I don't think it's a good thing. I think we've got to figure out a way to bring that number down."

The Lions made one change, as well, trying to help their 23rd-ranked defense by acquiring cornerback Johnthan Banks from the Tampa Bay Buccaneers. Banks was a college teammate of Detroit cornerback Darius Slay at Mississippi State and the two were second-round draft picks in 2013.

Banks will try to resurrect his career in a new spot.

Meanwhile, Minnesota is trying to prove its season isn't slipping away.

"I do think that we hit a rough spot in the season and we need to get back on track," Zimmer said. "So, unfortunately this is just some of the things that go on over the course of a season. Obviously, the season is a long time and not everything is going to go smooth, as I've found out over the three years. So, we'll just keep trying to do the things we have to do to continue to get better."