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Twice in Mike Zimmer’s seven offseasons as head coach, the Vikings have opened free agency with substantive investments that indicate how vital a run-stopping nose tackle is to their plans.

They made Linval Joseph the first free agent of the Zimmer era on March 12, 2014, giving the former Giants nose tackle a five-year, $31.25 million contract that would eventually be supplanted by a five-year, $62.5 million deal in 2017.

Those two deals put Joseph in the middle of the Vikings defense for 93 of a possible 101 regular-season and playoff games from 2014-19.

Then, when the team decided to move on from the 31-year-old Joseph this spring — releasing him six years and a day after it signed him — it made former Ravens tackle Michael Pierce its big prize of 2020 free agency with a three-year, $27 million deal.

Pierce’s decision on Tuesday to opt out of the 2020 season, over concerns about how COVID-19 could affect him given his family’s history with asthma, came with the blessing of team doctors who understood the risks coronavirus could present to the 345-pound tackle.

As of Wednesday afternoon, Pierce was one of 31 NFL players to forgo playing this fall, according to NFL.com, with the league’s opt-out deadline still at least a week away.

The NFL’s efforts to keep the virus out of locker rooms notwithstanding, football is laden with enough risk that players have more safety considerations than ever to weigh when determining whether to play or sit out this fall.

And yet, the choices players make for their personal well-being come with cold, empirical football effects. For the Vikings, it’s this: Without Pierce, they’ll head into the fall absent a proven nose tackle for the first time in Zimmer’s tenure.

They could look to add a veteran such as Damon Harrison or Domata Peko, who played for Zimmer in Cincinnati. But on Wednesday, indications were the Vikings would stick with what they have, confident in their ability to develop a young group of linemen as they’ve done so often under Zimmer and co-defensive coordinator Andre Patterson.

That route would mean opportunities for fourth-year tackle Jaleel Johnson, who posted career highs in sacks (3½), tackles (29) and tackles for loss (five) last year. The Vikings liked what they saw from Armon Watts at the end of the season, and new assistant defensive line coach Imarjaye Albury coached Watts at Arkansas. Shamar Stephen spent some time at nose tackle for the Seahawks in 2018, and he could do some work there if the Vikings feel good about a player like rookie James Lynch at the other defensive tackle spot.

But without the presence of a player like Joseph or Pierce, a spot the Vikings thought they’d solved for the 2020 season becomes another they will have to configure on the fly. They already have a new group of cornerbacks and a change at defensive end, barring a return from Everson Griffen, who remains a free agent.

“I know everybody is saying how it’s big turnover and all that,” Zimmer said in a conference call to discuss his three-year contract extension on Saturday. “We have lost some guys, but I think sometimes in these situations you forget about the guys you still have: Danielle Hunter, Pro Bowler; Anthony Barr, Pro Bowler; Eric Kendricks, a Pro Bowler; Harrison Smith, a Pro Bowler. We’ve got two really good safeties. We’ve got a good defensive line. We added Michael Pierce. We’ve got a really good group of linebackers. Obviously the corners are going to be younger, and that’s our job to bring them along as fast as we can.”

The same weekend Zimmer said those words, Pierce was flying to Minnesota to let the Vikings know of his decision in person. Pierce told the Star Tribune on Tuesday he would return to Alabama and “build the best home gym I can afford,” with plans to return in 2021 provided there’s a vaccine for the coronavirus by then.

If that happens, Pierce will cost the Vikings just $5 million against their 2021 cap, returning at age 28 with the potential to resume his career as the run-stopping force the Vikings have prized during Zimmer’s and Patterson’s time together in Minnesota.

Until then, a defensive coaching staff that prides itself on two things above all others — its resourcefulness and ability to coax the most out of players — has an unexpected chance to demonstrate both.

Ben Goessling • ben.goessling @startribune.com