The San Francisco 49ers made a surprise announcement that star running back Christian McCaffrey will not play in his team’s opening game against the New York Jets on Monday night.

What was a shock to everyone else, however, did not seem to be the case for his backup Jordan Mason, who could reveal after the 32-19 victory on “Monday Night Football” that the team violated an NFL rule.

Mason, who had an absolute career night in his first-ever start for the 49ers, spoke to ESPN’s Lisa Salters after totaling 147 rushing yards and a touchdown on 28 carries in the win when he said he knew he would be starting Friday in place of the injured McCaffrey.

CLICK HERE FOR MORE SPORTS COVERAGE ON FOXNEWS.COM

San Francisco 49ers running back Jordan Mason reacts after a run against New York Jets safety Chuck Clark during the fourth quarter at Levi’s Stadium. (Darren Yamashita-Imagn Images)

“When did I find out? Maybe Friday. Friday night, something like that,” Mason replied when Salters asked him when he found out he was on the starting line.

Mason also gave an interview after the game and seemed frustrated when another reporter asked him again when he found out he was in the starting lineup.

“That question is exactly why I’m angry,” he said. “That’s why I don’t like talking to the media, because you say one thing right and then, you know, I don’t know. Just skip that question.”

According to NFL Network, head coach Kyle Shanahan said after the game that Mason did not know he would be in the starting lineup, he was just told he would play a lot.

“He wasn’t sure until today if he was (in the starting lineup),” Shanahan said.

McCaffrey has been dealing with a calf/Achilles injury for the past few weeks, but expressed confidence that he could play against the Jets. That wasn’t the case just over an hour before kickoff, when the 49ers had to report their inactive players.

49ERS BEAT JETS, JORDAN MASON REPLACES INJURED CHRISTIAN MCCAFFREY

McCaffrey was listed as questionable prior to the game and the 49ers had not commented on his availability until the inactive players were announced.

So if Mason’s words are true and he learned on Friday that McCaffrey was unavailable to play and would still be in the starting lineup, then the 49ers would have violated an NFL rule by listing him as questionable when that was not the case.

Christian McCaffrey, No. 23, of the San Francisco 49ers runs the ball for a touchdown in the second quarter against the Kansas City Chiefs during Super Bowl LVIII at Allegiant Stadium on February 11, 2024 in Las Vegas. (Steph Chambers/Getty Images)

Of course, all NFL teams want to have an appropriate injury report to prepare for their opponents. However, with fantasy football and now legalized sports betting playing a major role in the NFL, injury reports are of utmost importance in determining lineups and betting on the right players.

“The information must be credible, accurate, current and specific within the guidelines, which is of paramount importance to maintaining the integrity of the game,” the league’s injury reporting policy states, according to Pro Football Network.

What will happen if the league investigates the situation and finds that the 49ers improperly reported McCaffrey? There will likely be a fine, but if the offense is serious enough, the NFL can also suspend players and force teams to forfeit draft picks.

One of the most notable such cases occurred in 2019, when the Pittsburgh Steelers failed to mention quarterback Ben Roethlisberger on a practice report. Rest was said to be the reason Roethlisberger did not practice on a Wednesday, but he left the game with a non-contact elbow injury that ultimately required season-ending surgery. He practiced on Thursday and Friday that week, but was not on the final injury report.

San Francisco 49ers running back Jordan Mason (No. 24) carries the ball against New York Jets linebacker Quincy Williams during the fourth quarter at Levi’s Stadium. (Darren Yamashita-Imagn Images)

CLICK HERE TO GET THE FOX NEWS APP

It will be interesting to see how the league responds to Mason’s comments.

Follow Fox News Digital Sports coverage on Xand subscribe the Fox News Sports Huddle newsletter.