You can’t really blame the San Francisco 49ers for deciding to make star running back Christian McCaffrey a late scratch for their season opener Monday night against the New York Jets.

The NFL’s reigning offensive Player of the Year has been dealing with calf and Achilles injuries and it makes absolutely no sense to use him until he is fully able to play without putting his leg at further risk. You don’t mess with an injury like that, especially when the words “Achilles” and “running back” appear in the same sentence.

But here’s the problem.

The 49ers clearly weren’t transparent about McCaffrey’s situation, and that opened a huge, ugly can of worms when it comes to the fantasy football crowd and legalized sports gambling on NFL games. Backup running back Jordan Mason was the steal of the night in betting circles.

The sportsbook prop “Jordan Mason to score the first touchdown” was 30-1 all weekend. After McCaffrey was declared “out” just 90 minutes before the game, that prop was moved all the way down to 6-1.

The 49ers hadn’t even added the Achilles description to McCaffrey’s status until Thursday, the first day they had to release their Week 1 injury report.

Despite participating in every practice session leading up to the game, albeit in a “limited” capacity, McCaffrey reportedly looked and ran around just fine, and he even proclaimed last Friday he was expecting to play and handle his usual heavy workload. That same day, San Francisco general manager John Lynch told KNBR Radio that CMC would “be out there and “ready to roll” against the Jets.

On Saturday, McCaffrey was officially listed as “questionable,” meaning there was a decent chance he would be active.

We know now there never really was a chance at all. That’s because after running wild for 147 yards and a touchdown during the 49ers’ 32-19 victory, Mason told us all the truth during a postgame interview with ESPN’s Lisa Salters.

She simply asked Mason when he knew he’d be starting.

“Maybe Friday. Friday night,” he told her. “Something like that.”

In the moment, right after the biggest game of his three-year pro career, Mason didn’t realize the significance of what he had just said.

It’s not his fault, though. The 49ers are the guilty party here. If Mason knew on Friday that he’d be starting, they knew it, too, and they should have ruled McCaffrey out on Saturday.

But they didn’t. Instead, the 49ers played loose with the rules and manipulated the league’s imperfect process for disclosing injuries and player status.

That’s a problem the league needs to solve. A select few — agents, family members and friends — have access to that inside information and could have made significant money before McCaffrey was declared inactive.

Betting props included the total (over/under) for Mason’s rushing yards, carries and receptions.

When the NFL decided to marry into the gambling industry, it immediately assumed the burden of making sure all injury designations were as accurate as possible. It’s not just legal wagering in sportsbooks: Millions of folks rely on accurate information for their fantasy football starting lineups.

The league’s injury report policy states, “The information must be credible, accurate, timely, and specific within the guidelines of the policy, which is of paramount importance in maintaining the integrity of the game.”

In the case of McCaffrey, the information about his availability wasn’t just incomplete, it was misleading. And when the 49ers officially declared him inactive just 90 minutes before kickoff at Levi’s Stadium, the news dropped like a bombshell.

In the locker room afterward, somebody obviously informed Mason not to tell anyone else what he had just told Salters on national television. That was evident in his response to a reporter’s question about when he learned he was going to be in the starting lineup in place of McCaffrey.

“That question right there is why I’m mad,” Mason replied. “That’s why I don’t like really talking to the media, because you say one thing wrong, and then, you know — I don’t know. Just skip that question.”

Coach Kyle Shanahan addressed the situation during his postgame news conference, but his answer left more questions.

“I never told Jordan he was going to start,” Shanahan said. “Told him he had to be ready a bunch. It might have been (running backs coach) Bobby (Turner) or somebody trying to pump him up. But I knew he was going to play a lot. Told him that it wasn’t going to be like usual.”

On Tuesday, Shanahan told reporters that the Achilles part of McCaffrey’s injury situation is related to tendinitis, adding, “That stuff comes and goes and when it is acting up, it’s something you’ve got to be careful about.”

Shanahan continued: “Christian is very diligent about that stuff. If it was a playoff game, he made it very clear to me he believed he could go. But when you hear that type of stuff, and it’s not a playoff game, and it’s Week 1, especially when you’re dealing with the lower extremities like that … in the long run it made (the decision to list him as inactive) easy.”

McCaffrey’s status this week for Sunday’s game at the Minnesota Vikings is “day-to-day,” according to Shanahan.

Take that for what it’s worth, especially if you’re thinking about placing a prop bet on McCaffrey or are considering starting him on your fantasy team.