SANTA CLARA, Calif. -- Two days after he was a surprise inactive in Monday night's season opener, San Francisco 49ers running back Christian McCaffrey explained how the decision to keep him out was made and why he was adamant on Friday that he would be available to play.

Speaking to Bay Area media before Wednesday afternoon's practice, McCaffrey attributed his confidence that he'd be able to play last week to the mentality he believes is necessary in such situations.

"My mindset every week is I'm going to play," McCaffrey said. "There's been weeks where I'll go the full week, not even feeling good enough to do the walk-through, and then I wake up and the body's capable of a lot of cool things. Mentally, I'm always prepared to play, and then I woke up and it was a group decision, a very tough one. I hate not playing but I look at it as a chess move and something that hopefully you can benefit from the rest of the season."

McCaffrey did not play against the New York Jets because of lingering calf and Achilles issues. Coach Kyle Shanahan explained Tuesday that the bigger problem for McCaffrey has been Achilles tendinitis because it comes and goes at varying degrees of severity.

Wednesday, Shanahan was asked whether there was any thought given to shutting McCaffrey down and placing him on injured reserve. Shanahan quickly shot that idea down.

"No, I've never considered that," Shanahan said. "We considered that he would play last week, so definitely not thinking about four weeks off."

Because the Niners played on Monday night, they will have fewer days to recover and prepare for Sunday's game against the Vikings in Minnesota. They were slated for a lighter practice on Wednesday afternoon, a practice in which McCaffrey is again expected to be a limited participant.

McCaffrey's injury first came to light as a calf issue when Shanahan announced it Aug. 6. It wasn't until last week when teams had to release an official injury report that the Achilles part was revealed. McCaffrey was a limited participant in practice all week, and when he spoke to media on Friday, he said he had no doubts he would play against the Jets and was even hopeful he would get his usual, heavy workload.

"I think when you don't feel right in practice there's a difference between you don't feel right, but maybe by Sunday you'll be good to go when you're working through some stuff and something's off," McCaffrey said. "My mindset is I'm going to play no matter what I'm going through physically on Wednesday or Thursday practice, and then the game day you've got to make a decision."

The calf injury is similar to the one McCaffrey had in a Week 17 win against the Washington Commanders last year, but he said Wednesday that this one is not a remnant of that one.

"It doesn't have anything to do with anything last season," McCaffrey said. "It's just something I'm dealing with that I'll get right."

As for this week, McCaffrey appears to be following a similar script as last week where there won't be any certainty on his status until closer to kickoff.

Because the Vikings play on artificial surface, there's been some question about how that might factor into the decision to play McCaffrey. If he has his way, it won't be a part of the discussion, with McCaffrey saying, "If you can go, you can go."

Just last season, McCaffrey played on the road against the Vikings after being listed as questionable and only practicing on a limited basis once because of an oblique injury. He went on to post 96 scrimmage yards and a pair of touchdowns in a 22-17 loss. If McCaffrey can't go, Jordan Mason will make his second NFL start. Mason replaced McCaffrey against the Jets, rushing 28 times for 147 yards and a touchdown. McCaffrey said Wednesday he was proud of Mason for performing so well on short notice.

Still, McCaffrey is unwavering in his belief that he is going to play, even if an official decision will again have to wait until closer to Sunday's kickoff.

"My mentality is I'm playing this week," McCaffrey said. "That's where I'm at. That's how I am every week. I'm not lying. I think as soon as a player says, 'maybe I'll play, maybe I won't,' that's not a good mentality to go into a week with when you're kind of on the fence. For me, I'm ready to go."