As his contract with the Ravens expired after the 2019 season and the potential of a big payday in free agency inched closer, Michael Pierce began making subtle changes to his routine in hopes of guarding against a virus that was just beginning its grip on American life.

He holed up with his parents near Mobile, Ala., working out in their attic. He stopped eating in restaurants in February, mindful of how pneumonia had racked his respiratory system during his second year with the Ravens and how his family's history with asthma could complicate things for anyone who contracted the coronavirus.

His father, Michael Sr., had been told to stay home from his job at the Mobile Public Housing Authority because of asthma, and Michael Jr. knew if he caught the virus, he could be putting himself and his family on a precipice.

"I'm one of those guys who took this thing seriously from the get-go because of my health," he said. "I just was up against the clock, man, so I had to make that call."

The call Pierce made in recent days, after signing a three-year, $27 million deal with the Vikings in March, was to put his football career on hold. The nose tackle flew to Minnesota to inform Vikings officials he would be opting out of the 2020 season, finalizing a decision he'd mulled for weeks as the virus raged on and the season neared.

Even before the NFL agreed with the NFL Players Association on a plan for players opting out of the 2020 season, Pierce, 27, said he was thinking about sitting out the year. He tuned in to every call the NFLPA held for players to stay up to date on how the season would look.

He talked to his childhood pediatrician, his family, his agent and the Vikings medical staff, who could refer back to the chest X-ray Pierce had received when he signed in March.

The choice that Pierce called "heartbreaking" Tuesday was also something of a consensus.

"It's something I've been battling my whole life," he said. "It's unfortunate. I'm really, really upset about it. I flew up here last night, and I just wanted to talk to everybody and make sure they understood I take this more seriously than I think some guys do. I'm super thankful they invested in me. If they get a vaccine, I'd love to be back out here in the spring, as soon as I possibly can. It's just an unfortunate time."

Pierce said he was "super shocked" when Vikings head athletic trainer Eric Sugarman tested positive over the weekend, adding that the virus is "just something that you can't predict."

"That's something [team doctor Sheldon] Burns told me, and he told me he definitely understood where I was coming from," Pierce said. "Just having a team official say that, it meant the world to me, because it let me know I was making the right decision."

The Vikings had signed Pierce to replace Linval Joseph as a run-stopping force in the middle of their defensive line, and his absence leaves a significant gap in middle of the Vikings' front. Jaleel Johnson and Armon Watts could be asked to take on bigger roles, and the Vikings could pursue another veteran lineman to help take Pierce's place.

Because Pierce's history of asthma made him a high-risk case, he will receive a $350,000 stipend. His contract will toll, meaning his deal will run through 2023 and the Vikings should only have to count $2 million of Pierce's signing bonus and the $350,000 stipend against the cap in 2020.

In the meantime, he said, he'll return to Birmingham and build "the best home gym I can afford" to stay in shape for the 2021 season, working with the staff at Samford (where Pierce played in college) on a training program he could either do on his own or with a trainer who's tested negative for COVID-19.

He isn't sure yet if the NFL and NFLPA have agreed on parameters that will allow him to attend team meetings, but if he's able to do so, Pierce said, "I'll be there 110 percent."

Pierce's hopes for next season hinge somewhat on the efficacy and availability of a vaccine, which remains unknown at this point. He took solace in conversations with Vikings doctors who sounded optimistic about the potential for a vaccine by 2021, but even then, he acknowledged, "we don't know how effective it will be."

Logic drove his decision for the 2020 season. Hope fuels his outlook for 2021.

"I love this game, man. I'm heartbroken that I'm letting a lot of people down right now," Pierce said. "I bought a POD [storage unit], and I'm storing it here. Until they tell me again that I cannot come out there, I will try everything possible to get back."