INDIANAPOLIS -- Mike Zimmer spent most of his 21 years in the NFL as a defensive coach, so it is no surprise where he focused his attention in his first 35 days as head coach of the Minnesota Vikings.

"Any time you finish 31st in the league, you've got quite a few holes," Zimmer said of the Minnesota defense, which was worst in the NFL in points allowed. "We're going to need quite a few good football players."

Zimmer hinted that the Vikings' personnel is versatile enough to use multiple fronts. He coached the 3-4 defense with the Dallas Cowboys and a 4-3 as defensive coordinator of the Cincinnati Bengals.

Defensive end Jared Allen, an unrestricted free agent, would not fit as an outside linebacker. He is limited laterally but explosive off the ball. If the price is right, the Vikings would still like to bring him back. Other moving parts on the depth chart in the front seven are edge rusher Everson Griffen, defensive tackle Kevin Williams -- a prime five-technique defensive end candidate in a 3-4 alignment -- and defensive tackle Fred Evans.

"It's all about getting the right players that fit the system we're looking for," Zimmer said when asked specifically about Allen, who turns 32 next month. "We'd love to sign all of our guys. We understand that we're not going to be able to sign them all. Hopefully we can get worked out with him, and we'll see as it goes."

General manager Rick Spielman described Zimmer as a grinder who is leaving no stone unturned in assimilating to his first ever head coaching job, even making it look natural. Zimmer said there are still some rough edges to smooth out in the new routine and additional responsibilities that come with being the all-powerful coach on staff.

"The biggest thing for me right now has been the schedules," Zimmer said. "It's just a pain in the rear end that you're trying to do schedules for training camp -- when to do red zone, when to do all the situations that come about. That is a part that has been difficult for me."

He said the Vikings are not ruling out keeping quarterback Christian Ponder, but wants to see him on the field before deciding where -- and if -- he fits in Minnesota moving forward.

"He's got a great arm, he runs good, he's a bright guy," Zimmer said. "Everyone wants him to live up to expectations. ... I'm not a patient person with anybody. I just think once we get on the field we'll figure all those things out."

Spielman said Thursday the Vikings will meet with Matt Cassel's agent. Cassel ended the season as the starter but opted out of the second year of his contract.

With or without Cassel, could Ponder be the starter for the Vikings in 2014?

"If he's the best player," Zimmer said.