Christian McCaffrey is out for the 49ers’ matchup against the Vikings on Sunday — and possibly longer.

San Francisco head coach Kyle Shanahan told reporters Friday that the star running back will miss Week 2 and that the team is considering placing him on the injured reserve list as he deals with a lingering calf/Achilles injury.

McCaffrey missed the 49ers’ season opener against the Jets on Monday as a last-minute scratch that put backup Jordan Mason, who rushed for 147 yards in the 32-19 victory at home, into the starting role.

The 49ers were hopeful that McCaffrey could take the field in Minnesota, but Shanahan said he had his “worst day” with the injury on Thursday, per ESPN, taking that possibility out of the picture.

Shanahan said this week that McCaffrey’s injury “comes and goes,” and that the team was playing the long game with the reigning Offensive Player of the Year.

“It’s not just the calf, it’s the Achilles, and the Achilles is tendinitis, and that stuff comes and goes. And when it is acting up it’s something you’ve got to be very careful about,” Shanahan said, per Pro Football Talk.

If the team places him on IR, McCaffrey will miss Sunday’s game and the next three weeks — at minimum.

Mason, who signed with the 49ers as an undrafted free agent in 2022, would presumably continue his role as the team’s starting running back after his strong Week 1 performance.