Sep 9, 2024; Santa Clara, California, USA; San Francisco 49ers head coach Kyle Shanahan chats with a reporter before a game against the New York Jets at Levi's Stadium. / David Gonzales-Imagn Images

In a newsworthy weekend for the football world, San Francisco 49ers running back Christian McCaffrey being ruled out right before kickoff against the New York Jets Monday still managed to make waves.

Much speculation surrounded the precise nature of McCaffrey's injury -- especially when 49ers running back Jordan Mason suggested after his team's 32-13 win that he knew he would replace the superstar on Friday. On Tuesday, San Francisco coach Kyle Shanahan offered a more thorough assessment of McCaffrey's status -- calling him day-to-day.

"The Achilles tendonitis and that stuff comes and goes. And when it is acting up, it's something you've got to be very careful about. Christian's very diligent about that stuff," Shanahan said via Nick Wagoner of ESPN. "And if it was a playoff game, he made it very clear to me he believed he could go."

McCaffrey has battled injuries on and off throughout his professional career -- he played just 10 games from 2020 to '21, for instance -- and missed the preseason with what the 49ers called a calf and Achilles injury.

"When you hear that type of stuff and it's not a playoff game and it's week one and especially when you're dealing with the lower extremities like that, it was a tough decision, but hearing all the words in the long run, it made it easy," Shanahan explained.