MINNEAPOLIS – The San Francisco 49ers have placed star running back Christian McCaffrey on the injured list due to calf soreness and Achilles tendonitis, the team announced Saturday.

McCaffrey will miss at least the next four games – including Sunday’s game against the Minnesota Vikings – and is eligible to return for a meeting with the Seattle Seahawks on Thursday Night Football on Oct. 10, but that is not guaranteed.

On Friday, San Francisco coach Kyle Shanahan acknowledged that injured reserve was a real possibility for the first time since McCaffrey’s injury was first announced on Aug. 6. This came after McCaffrey’s Achilles tendon did not respond well to limited practice participation on Thursday.

“Yesterday was his worst day,” Shanahan said. “It’s hit or miss, but yesterday was the worst pain he’s ever had. That’s something we’ll discuss together over the next 24 hours.”

Those discussions ultimately led to Saturday’s decision to sit McCaffrey out in hopes that lingering Achilles pain would settle down. Shanahan said the worst thing about McCaffrey’s injury was its unpredictability, with the running back feeling fine and practicing on some days but in pain on other days.

Landing on the injured list is undoubtedly a disappointment for McCaffrey, the reigning NFL Offensive Player of the Year. He announced on Wednesday that he would play against the Vikings and said he is determined to be ready to play each week, even if he is battling an injury.

“I hate not playing,” McCaffrey said Wednesday. “But I see it as a move and something that hopefully will benefit the rest of the season.”

This IR stint is McCaffrey’s first since joining the 49ers via trade in October 2022. Including the postseason, McCaffrey had missed just one of a possible 33 games over the past two seasons, with the lone missed day being a meaningless Week 18 game against the Los Angeles Rams, in which McCaffrey was dealing with a calf injury but both teams were resting their starters anyway.

Before arriving in San Francisco, McCaffrey struggled with injuries as a member of the Carolina Panthers. In 2020 and 2021, McCaffrey played in a total of 10 games and missed games due to a high right ankle sprain, a sprain of the AC joint in the shoulder, a glute and hamstring strain, and a left ankle sprain.

With McCaffrey out, Jordan Mason will assume primary running back duties after making his first career start last week against the New York Jets. Mason finished the game with 28 carries for 147 yards, both career highs, and a touchdown. It was the most carries by a Niners player in a regular season game since Shanahan took over in 2017 and the most in a 49ers season opener in franchise history.

Against the Jets, the Niners used wide receiver Deebo Samuel Sr. as Mason’s primary backup. He had eight carries for 23 yards and a touchdown. Other running back options for the 49ers include rookie Isaac Guerendo and fourth-year veteran Patrick Taylor Jr. on the active roster and fifth-year veteran Ke’Shawn Vaughn on the practice squad.

The 49ers have yet to fill McCaffrey’s spot on the 53-man roster.