Sheldon Richardson's 2021 season — his second with the Vikings and ninth in the NFL — is thus far the first in the defensive lineman's career where he hasn't started a game.

That could change on Sunday, as the Vikings give Richardson an enhanced role on a defensive front that lost two more starters this week.

Dalvin Tomlinson will miss the game at San Francisco while on the COVID-19 reserve list, and Everson Griffen could be away from the Vikings for some time after he was taken by ambulance from his home to a mental health facility on Wednesday.

Their absences, coupled with injuries to Danielle Hunter and Michael Pierce, mean the Vikings will be without each of their four preferred starters on the defensive line heading into a matchup with the 49ers that should be pivotal for playoff positioning.

Enter Richardson, who was brought back for a second stint in Minnesota last June after spending two seasons with the Browns. The Vikings gave him a one-year, $3.6 million deal with the idea he would provide an interior pass-rushing presence, but in light of their absences up front, they have asked him to play a different role.

"He's going to play every place. He's going to play inside, he's going to play outside," Vikings co-defensive coordinator Andre Patterson said. "He's proven he can go out there and play on the edge and give us a chance to be successful and win. He played both spots on Sunday. I kind of see that happening again on Sunday."

The Vikings have increased Richardson's number of snaps at defensive end the past two weeks, playing him there for most of his 34 snaps against the Packers. He had a pair of pressures on Aaron Rodgers, teaming with D.J. Wonnum to force an incompletion on a third down before Mason Crosby's missed field goal.

Richardson spent some time at defensive end for the Browns last season, and played everywhere from defensive end to outside linebacker in the Jets' 3-4 scheme when he entered the league. Though this season is his first in Minnesota since 2018, he is familiar enough with the Vikings defense to shift without many issues, he said.

"I've been playing football for a long time, going back to my high school days," Richardson said. "I feel like I knew the schemes around here, pretty much knew the playbook already coming in. Just had to get ready for the trigger words I'm not used to hearing, going from 3-technique to D-end. It really helped me out a lot. Just knowing football, and knowing the scheme, and knowing Zim's system, it's kind of easy to play in."

Richardson, Patterson said, is "athletic enough to go out on the edge and not feel out of place," pointing out the way he was able to pressure Packers right tackle Billy Turner with speed while keeping his leverage against Turner's pass sets.

"He's a 300-pound guy that was running and coming back downhill on him," Patterson said. "For some big guys, it's hard to be out there in space like that, but Sheldon was comfortable doing that, and I thought he did a tremendous job for us last Sunday."

The Vikings brought back Tashawn Bower for a second stint in Minnesota by claiming him off the Patriots' practice squad this week, and they also recently returned Eddie Yarbrough to their roster for a second time. They will be helped, coach Mike Zimmer said, by the fact they have got plenty of familiarity with the Vikings defense as they try to step into bigger roles.

Of the linemen who have returned to Minnesota after going somewhere else, none might be more important this week than Richardson. The Vikings will need help against a 49ers team that wins by exerting its will up front.

"Well, first of all, I wouldn't use the term depleted. I don't look at it that way," Patterson said. "This is a football team. Like I've said before, you prepare everybody to get a chance to play. You never know. Injuries happen in this game, and in the COVID era and the way it is, other guys get a chance now to step up and play.

"The San Francisco 49ers are not going to feel sorry for us. I don't feel sorry for us. We're going to go compete. That's who I am.

"We're going to go compete and we're going to go play for 60 minutes and find a way to win the game. That's why we're going. Whoever puts on a purple helmet and goes out there and plays for me is going to give me everything they've got for 60 minutes, and we're going to find a way to win the game. That's how I approach it."