SANTA CLARA, Calif. -- There's no mystery surrounding the status of San Francisco 49ers running back Christian McCaffrey this week.

Niners coach Kyle Shanahan confirmed on Friday that McCaffrey will miss Sunday's game against the Minnesota Vikings . McCaffrey was limited in Thursday's practice, but wasn't feeling right. Shanahan mentioned that placing McCaffrey on injured reserve, which would require him to miss at least four more games, is now being considered.

"We're considering that option," Shanahan said. "Yesterday was his toughest day. The pain comes and goes, but yesterday was particularly bad. We'll talk about it in the next 24 hours."

McCaffrey has been dealing with a calf injury and Achilles tendinitis. These injuries led to his unexpected absence before the Monday night opener against the New York Jets .

Similar to last week, McCaffrey had limited participation in Wednesday and Thursday's practices. However, his absence from the field during the media portion of Friday's practice hinted at his potential unavailability.

If the Niners place McCaffrey on injured reserve before Sunday's game in Minnesota, he would be eligible to return for the Oct. 10 game against the Seattle Seahawks on "Thursday Night Football." Shanahan added that, as of now, McCaffrey doesn't require surgery for the injury.

On Wednesday, McCaffrey addressed the media and explained his determination to play against the Jets, despite the injury. He revealed that his mentality when dealing with injuries is to always believe he'll be ready, even if reality dictates otherwise.

"My mindset every week is that I'm going to play," McCaffrey said on Tuesday. "There have been weeks when I've gone through the entire week, not even feeling well enough to participate in walkthroughs, but then I wake up and my body is capable of amazing things. Mentally, I'm always prepared to play, and then I woke up and it was a collective decision, a very tough one. I hate not playing, but I see it as a strategic move, something that could ultimately benefit us for the rest of the season."

The 49ers are hoping that more rest for McCaffrey will allow him to overcome the tendinitis. Shanahan has stated that the Achilles issue is unpredictable, making it challenging to assess his condition on anything other than a daily basis.

Shanahan was asked on Wednesday if McCaffrey might be placed on injured reserve with the possibility of returning after missing four games. He dismissed that possibility then, but he and general manager John Lynch changed their tune on Friday after McCaffrey's setback on Thursday.

"If that's the right course of action, it's what we'll do," Lynch told KNBR Radio in San Francisco. "We're exploring all options, as Kyle has mentioned. We'll make the best decision for Christian and for our team."

This week, that means a second consecutive start for third-year running back Jordan Mason following his breakout performance against New York. In his first career start, Mason carried the ball 28 times for 147 yards and a touchdown, adding a 5-yard reception. It was the highest number of carries in a regular season game by a Niner since Shanahan took over in 2017 and the most in a 49ers season opener in franchise history.

That performance undoubtedly boosted San Francisco's confidence in Mason's ability to lead the team as they travel to Minnesota, a venue where the Niners have suffered seven consecutive defeats.

"I continuously emphasize, this guy just keeps improving consistently," run game coordinator Chris Foerster stated. "JP has always been diligent in his work, but there was always a slight element of uncertainty regarding his reliability. Now he's fully committed to (running backs coach) Bobby (Turner) and the offense, and he's thrived. He's a tough and determined runner."

With McCaffrey sidelined and Mason taking over as starter, the Niners' backup options for running back will once again include wide receiver Deebo Samuel, rookie Isaac Guerendo and fourth-year veteran Patrick Taylor Jr . However, neither Guerendo nor Taylor carried the ball behind Mason against the Jets. Samuel was the only other Niner to take a handoff, running the ball eight times for 23 yards and a touchdown.

"It's unusual to be down to our third option already," Shanahan mentioned. "I've never considered Elijah (Mitchell) or JP (Mason) as merely backups. I believe they both have the potential to be starting caliber players, as Elijah has demonstrated in the past and so did JP. The two new additions, when their opportunity arises, I'm confident they're prepared."

In other 49ers injury news, safety Talanoa Hufanga (right knee) is doubtful for Sunday and linebacker Dee Winters (ankle) is listed as questionable.