They have already replaced offensive line coach Jeff Davidson with former Dolphins head coach Tony Sparano. With uncertainty at all five spots along the offensive line, personnel changes will be coming, too.

At left tackle, Matt Kalil had a promising start to the season and his play was better compared to 2014. But 2015 ended up being the third straight subpar season for the fourth overall draft pick in 2012. He is under contract through 2016. This will likely be his last chance to show he is a long-term solution, unless the Vikings decide to cut ties with him this offseason. After all, he has an $11.1 million cap hit.

At left guard, Brandon Fusco could not replicate the success he had at right guard a couple of seasons ago. He missed most of the 2014 season with a torn pectoral and then moved to left guard in 2015, where his play didn't match his pay. Fusco figures to be a starter again next season, but perhaps the Vikings will move him back to his old spot at right guard.

At center, John Sullivan had a pair of back surgeries in 2015 and missed the entire regular season. He is under contract through 2017, but the Vikings could part ways with him with minimal cap repercussions. My guess is they will give Sullivan a chance to reclaim his starting job from Joe Berger, but it is fair to wonder if the 30-year-old center will ever return to form.

At right guard, Mike Harris is an unrestricted free agent. He had played tackle for pretty much all of his life before the Vikings moved him to guard at the start of training camp. He ended up holding his own there, but tackle is probably his ideal position. It is unknown whether the Vikings feel the same way about that or if they think he is worth keeping around.

At right tackle, Phil Loadholt is trying to work his way back from a torn Achilles' tendon. That injury is hard to recover from, especially when you are 30 and weigh 330-plus pounds. He could end up being a cap casualty. Meanwhile, rookie T.J. Clemmings started all 16 games in his place but often struggled. Coach Mike Zimmer made it clear he will have to earn a starting job in 2016 then indicated that everyone else would have to, too.

As far as the backups go, Carter Bykowski, Nick Easton, Zac Kerin, Austin Shepherd and Jeremiah Sirles are expected to be back in 2016. They came to Minnesota in different ways, but they are all young, unproven players who were late-round picks or went undrafted.

That fits a trend I wrote about back in November. The Vikings have only drafted two offensive linemen in the first three rounds of the draft since 2007. That would be Kalil and Loadholt. It has been their preference to take late-round flyers on players and hope to develop them over time. That approach worked in the past with Sullivan and Fusco, who became solid starters. But it came back to bite them this season.

This offseason, the Vikings will have to be more proactive when it comes to rebuilding the line, and the good news is it sounds like they plan to be.

I haven't had a chance to do much homework on the 2016 draft class, but there could be several solid options available in free agency, including tackles Russell Okung, Andre Smith, Cordy Glenn and Donald Penn and guards Evan Mathis, Alex Boone, Ramon Foster and Richie Incognito.

Of course, it has been General Manager Rick Spielman's preference to build through the draft. We'll see if Spielman and Zimmer feel the offensive line is a concern pressing enough to make a significant move in free agency.

But whether they do it through free agency, the draft or both, something needs to be done to prop up the offensive line to give quarterback Teddy Bridgewater a chance to take the big step forward we didn't see in 2015.