The Vikings invested $11 million in Matt Kalil last spring, and coach Mike Zimmer liked the early preseason returns from tweaked footwork in pass protection sets.

Then Kalil injured his hip in practice, starting the left tackle down a path leading to surgery and 14 games on injured reserve. The hefty bet on making one more evaluation on Kalil as a long-term solution fell flat.

Now, the Vikings have a hole at left tackle with no heir apparent on the current 2017 roster. So where does that leave Kalil, a pending free agent, and the Vikings?

An improved running game and a more explosive passing game top the Vikings' priority list on offense, coordinator Pat Shurmur said last week at the team's WinterFest in Prior Lake. How the Vikings achieve that will undoubtedly start along last year's tattered offensive line. Shurmur declined to get into specifics about Kalil.

"Certainly anything you do on offense starts up front," Shurmur said. "So obviously there will be changes at all the position groups."

What's clear is the Vikings' need at tackle is dire, it faces a draft with little fanfare at tackle and the reality that proven left tackles don't become available very often.

Cincinnati's Andrew Whitworth, ahead of his age 35 season, looks like the market's top potential option, should he even reach free agency as the Bengals reportedly sought to discuss a new deal with Whitworth this month. Denver's Russell Okung and Miami's Brandon Albert are other veterans currently under contract who could be made available next month. A trade is another route, though swaps can't be made official until the new league year begins March 9.

The Vikings have had a propensity to bet on the known over the unknown under General Manager Rick Spielman by keeping many deals, whether lucrative extensions or prove-it contracts, for their own players.

What that means for Kalil's future in Minnesota remains to be seen, but his return shouldn't be counted out.

Pending free agent left tackles

-Andrew Whitworth (Bengals), age 35

Even though Whitworth turned 35 in December, the Bengals tackle is coming off perhaps his best seasons in the past two years, which include two Pro Bowls and a first-team All-Pro selection. Don't overlook his durability. Whitworth hasn't missed a game since 2013 and has sat out just eight games in his 11-year career.

-Riley Reiff (Lions), age 28

A lackluster left tackle market could have some thinking about Reiff moving back to where he started 47 of 48 games for the Lions from 2013 to 2015. Detroit moved Reiff to right tackle last season following the first-round selection of Taylor Decker. He's missed just three starts in the last four seasons and could land a significant contract this spring as a versatile edge protector.

-Ty Nsekhe (Redskins), age 31

The Vikings saw firsthand Nsekhe's play at left tackle when Everson Griffen went without a sack in their Nov. 13 meeting. Nsekhe, a 31-year-old journeyman, has just six career starts, but he made a strong case in four of them last season during Trent Williams' suspension. Nsekhe was active for 16 games last season while dealing with a nagging ankle injury.

-Kelvin Beachum (Jaguars), age 27

Unlike Nsekhe, the Vikings' Griffen had little trouble breezing past Kelvin Beachum in Jacksonville last season. The game exemplified a down season for Beachum, the 27-year-old former seventh-round pick by the Steelers. He's just a year removed from a torn ACL, which ended his run as a starter in Pittsburgh, and could be worth a look for the tackle-needy Vikings.

-Ryan Clady (Jets), age 30

The former All-Pro left tackle for the Broncos has had tough luck the past four seasons, starting 16 games only once. Clady appeared in nine games with the Jets before a torn rotator cuff put him on injured reserve. The Jets declined Clady's 2017 option, so he's a free agent. Talented and injury-riddled, Clady has missed 37 games due to Lisfranc, ACL and shoulder injuries the last four seasons.

Also: William Beatty (Giants), Ben Ijalana (Jets), Bradley Sowell (Seahawks)