49ers star running back Christian McCaffrey has been ruled out due to his calf injury and Achilles tendonitis, head coach Kyle Shanahan announced on Friday. It’ll be Jordan Mason at running back for San Francisco for a second consecutive week this Sunday against the Vikings.

McCaffrey also missed the 49ers’ opener against the Jets, a game in which Mason had 152 yards from scrimmage and a touchdown on 29 touches. He said this week that his mentality was to prepare like he’s going to play, but clearly, the 49ers are taking a cautious approach with one of their best players. Shanahan said a trip to injured reserve isn’t out of the question for McCaffrey.

That’s a big loss for the 49ers. McCaffrey was the NFL’s Offensive Player of the Year last season after racking up over 2,000 yards from scrimmage and 21 touchdowns. He’s one of the most dangerous running backs and offensive weapons in the league. Mason is a quality backup, but the Vikings won’t be upset about not seeing McCaffrey on the other side of the ball this weekend.

Safety Talanoa Hufanga, a 2022 first team All-Pro, is doubtful for the 49ers. He also missed last week’s game. Backup linebacker Dee Winters is questionable. Jauan Jennings, who was SF’s leading receiver a week ago, will play despite dealing with an injury this week in practice.