The NFL Combine officially gets underway Thursday at Lucas Oil Stadium in Indianapolis. And while the hype of the event will center mostly around the 40-yard dash times, bench press reps and shuttle runs of the more than 300 draft prospects invited to participate, some of the most significant action of the week occurs behind the scenes as NFL general managers and front office personnel meet with agents to begin discussing the approach of free agency.

At this stage, league rules state that teams are only allowed to talk with the agents of their own players. So with the Vikings needing to make decisions on 10 unrestricted free agents who are scheduled to hit the open market March 12, here's our quick update on where we think things might be headed.

Today, we look at the team's four defensive free agents. (And in case you missed it, here's Monday's look at the Vikings' UFAs on offense.)

Jasper Brinkley

The preseason worries that Brinkley might be a major liability up the middle of the defense didn't last long. After shaking off the rust in the preseason, Brinkley put his 2011 hip injury behind him and quickly flashed his strengths as a guy who can get downhill in a hurry and be a solid force against the run. His 117 tackles ranked third on the team behind Chad Greenway (191) and Harrison Smith (129). But it didn't help that the 27-year-old Brinkley saw his effectiveness dip when he was asked to play extended snaps as the Vikings' MLB in nickel packages. By season's end Erin Henderson had reclaimed those responsibilities and Brinkley hadn't lessened worries that he has deficiencies dropping in to coverage.

The likely move: In order to take the next step as a defense, the Vikings will need to find a number 2 linebacker who can fully complement Greenway. And they certainly need to find a guy who can have maximum productivity playing every down. So now, with Brinkley, Henderson and Marvin Mitchell all nearing free agency, the team faces the risk of losing three of its top four linebackers from 2012. It's unlikely all three players will get away. In fact, it would not be a surprise if at least two of them are back. But the Vikings will also assess what could be available for them in free agency and the draft. In other words: the final decision on Brinkley depends on several other moving parts.

Erin Henderson

Déjà vu. Henderson was an unrestricted free agent last year, too. But it took 10 days after the market opened for him to re-sign with the Vikings. Henderson was peeved at that time that he hadn't been offered a bigger pay day – by anyone. But the Vikings did the right thing in allowing the market to set the appropriate price. What resulted was a one-year deal with a base salary of $1.45 million. Henderson hoped to then have a big 2012 season and land a much, much bigger deal. So here we are again. Who knows how much last year's foray into free agency has altered Henderson's mindset? But he best be realistic with what he's worth as he seeks out his best opportunity.

The likely move: Henderson's 2012 stats: 112 tackles, 10 tackles for loss, three sacks and a forced fumble. He was solid overall. But Patrick Willis he is not. And he still suffers from moments when, in his own words, his eyes get too big and he tries to make plays that either aren't his to make or just aren't there. (See: the 5-yard touchdown catch Green Bay's Greg Jennings made in Week 17 with Henderson inexplicably releasing Jennings to run uncovered into the end zone.) As we mentioned, Henderson is one of three Viking linebackers headed for free agency. So all three of their situations will in some way be intertwined. Brinkley and Henderson are both represented by Sportstars, Inc., which theoretically should eliminate some of the guesswork on that side of things for how the Vikings are viewing the pecking order. Right now, Brinkley may get the edge as a better bargain. But it's also quite possible Henderson is brought back.

Jamarca Sanford

One of the surprise contributors of 2012 should see his hard work and high energy rewarded. After losing his starting job as a safety in training camp, Sanford returned to that role in Week 4 after Mistral Raymond dislocated his ankle. And the 27-year-old Sanford started the rest of the way – though he did finish the season sharing time with Raymond. He's still a bit small (5-foot-10, 200 pounds) and sometimes deficient in pass coverage. But Sanford compensates for his handicaps with his work ethic.

The likely move: The Vikings' long-term plan seems to be for Raymond to emerge full-time as the second starting safety alongside Harrison Smith. But Sanford's value as dependable depth should not be taken for granted. While he may never ascend to be a major playmaker, he's exactly the kind of player the Vikings coaching staff and front office wants to build around. He's unselfish, he's low maintenance, he's passionate and he's willing to invest to get better. Add into the equation that he's always been a terrific special teams player and there has to be a spot open for Sanford to come back. In fact, safety and running back are probably the two positions the Vikings could afford to leave untouched as they transition from 2012 into 2013.

Marvin Mitchell

With Henderson sidelined by a concussion in September, Mitchell started twice and aided solid defensive performances in wins over the 49ers and Lions. He was also a dependable contributor on special teams. It's no secret that the Vikings depth at linebacker right now is average at best. With Brinkley, Henderson and Mitchell all approaching free agency, that leaves Chad Greenway, Tyrone McKenzie, Larry Dean and Audie Cole as the only linebackers signed for 2013.

The likely move: Of all the Vikings UFAs, Mitchell's case shouldn't draw much more than a shrug and an "Hey, either way" reaction. Like offensive lineman Joe Berger, if he returns great. And if he doesn't, his spot shouldn't be difficult to fill. Mitchell would love to come back if it's the right situation. And he seemed to fit in well within the locker room in 2012. Henderson and Brinkley will be the first pieces of the linebacker puzzle that need to be figured out. But Mitchell would be an easy guy to keep in the mix.