Minnesota Vikings general manager Rick Spielman is slowly building an impressive roster that should soon be a serious threat in the NFC North. Aside from left tackle Matt Kalil and wide receiver Cordarrelle Patterson, who could both still end up being consistently productive players, Spielman has been lauded for his draft returns. Nowhere is this more evident than second-year quarterback Teddy Bridgewater whose impressive rookie year has Vikings fans very excited.

But Minnesota won't be able to get the most out of Bridgewater if they don't improve up front along the offensive line.

"However, protecting Bridgewater was an issue for Minnesota, which ranked 27th in adjusted sack rate," Sterling Xie of Football Outsiders wrote. "Much of that stemmed from Kalil's struggles and season ending injuries to Brandon Fusco and Phil Loadholt, but all three will be back and presumably starting in 2015.

"Depending on how Kalil bounces back after offseason surgeries on both knees, the Vikings' biggest hole along the offensive line may actually be at left guard, where four-year starter Charlie Johnson was released in the offseason. Johnson has largely earned apathy for subpar play, and while he's someone you'd hope to upgrade from in the long run, the 31-year-old was one of the few Minnesota linemen who were both consistently available and passable. Last season, our game charters marked Johnson down for a blown block once every 62.4 snaps, fourth-best among Minnesota linemen and a general middle-of-the-pack rate among all offensive linemen."

Overall, the Vikings suffer from a lack of quality interior line depth. Fourth-rounder T.J. Clemming and sixth-rounder Tyrus Thompson may prove to be viable options down the road, but neither is ready to start in Week 1.

Minnesota surrendered 51 sacks and 96 total QB hits in 2014, far too many for Bridgewater's slight frame to endure again. To maximize his potential, Spielman may want to more heavily invest in the offensive line in the years to come.