EDEN PRARIE, Minn. – Minnesota took many steps to ensure that the core players on defense will be with the team for the long term this offseason.

Contract extensions to defensive end Everson Griffen, cornerback Xavier Rhodes and defensive tackle Linval Joseph all during training camp signified that the Vikings front office is buying into keeping the key contributors together for years to come.

Vikings Head Coach Mike Zimmer is entering his fourth year at the helm and with each of those players and several others. He recognizes that he and his staff have to continue to develop and try new things so his veterans don't become too complacent.

Zimmer figures that the preseason is a great time to do so.

"I was talking to [Vikings Owner/President] Mark Wilf a little bit today, and these guys have been around the system, and so the install, they have seen it four times," Zimmer said. "So to get them excited about something new, we have to keep being innovative as coaches. We're still looking at things where we can get better defensively."

Zimmer said there are plays he has called and tried out during the preseason that he wouldn't call during the regular season. He noted that a few defensive plays against the run were ones that he was testing out and trying to innovate.

"Some of the things that happened in the game (against Seattle), or the first game, if we don't like, we'll throw them out," Zimmer said. "I just want to make sure that those guys understand the way we have played around here on defense is with a chip on our shoulder."

Zimmer approaches the preseason games by focusing on the development his team. He doesn't game plan for the opponent, and he won't be game planning for the 49ers this week.

"I've never really felt the need to game plan in the third game," Zimmer said. "We just go out there and do what we do. I think it's good to see how the team reacts to scenarios that they are not prepared for. That's kind of how we've done it since we've been here. We still have work to do on us, so for us to take a week and work on San Francisco like we would in a season game, I think it is counter productive."

Here are three other topics addressed by Zimmer:

1. Progress on the offensive line

The Vikings first unit did not allow a sack of Sam Bradford in an improved showing against Seattle in the second preseason game.

After gaining 34 yards of total offense in the first preseason game against Buffalo, the Vikings first-team offense gained 123 yards against the Seahawks, which could signal that the offensive line is moving in the right direction.

"The offensive line came off the ball low and physical," Zimmer said. "I thought they did a good job with a lot of those things," Zimmer said. "I guess it's the things in practice. We had a red zone period the other day, and they scored a bunch of times on different plays. Until we do it on the field, it's just about what I see in practice."

In practice Zimmer continues to fiddle with the five players that he has running with the first unit on the line.

Third round draft pick Pat Elflein continues to battle with Nick Easton for the starting center spot, while the two have each seen some time at the guard position.

"Pat is a very good athlete," Zimmer said. "He's physical at the line of scrimmage and for the most part makes all the right calls. I guess the thing I like the most about him is he's able to finish the blocks. When he gets on a guy he can move him with his low center of gravity and wide base."

2. Thielen in slot

Adam Thielen led the Vikings in receiving yards (967) in 2016 and quickly developed chemistry with Bradford as a wide receiver on the outside.

In practice and in the game, Thielen has started to take reps in the slot position.

Zimmer continues to stress the stronger communication between him and the offense and sees Thielen as a weapon on the inside.

"I've talked to Sam about all of those things," Zimmer said.  "I think he feels really comfortable about trusting [Thielen] in where he's going to be in a lot of the option routes and some combinations that they have between the slot and the tight end or between the slot and the [outside] receiver. I think Adam has a good feel in there, and I think Sam trusts him."

3. Tough roster decisions

Zimmer will have to make all of his roster cuts after the final preseason game as the roster will shrink from 90 players to 53.

With a mix of core veterans and supply of youth, the head coach will have his hands full deciding which 53 players will suit up for the home opener on Sept. 11 against the New Orleans Saints.

There are a few positions where Zimmer has his eyes on rookies, and on Wednesday he noted the defensive line.

"There are several spots where we are going to have some tough issues, and that's why it's good to have the fourth preseason game to get a chance to see them in that game as well," Zimmer said. "This week will be a big week again for a lot of these guys."

"Some of these young defensive lineman have looked good," Zimmer added. "Jaleel Johnson has had good ball games. Ifeadi (Odenigbo) has done a nice job in some areas. [Tashawn] Bower and [second-year pro Stephen] Weatherly have done good. They are showing some things that could be valuable for us down the road."