San Francisco 49ers running back Christian McCaffrey is out for Monday's game against the New York Jets with a calf injury.

The 49ers announced McCaffrey's status in the team's inactives report shortly before kickoff. Former All-Pro safety Talanoa Hufanga is also among San Francisco's inactives with a lingering knee injury that sidelined him at the end of last season. Jordan Mason will get the start at running back.

Will McCaffrey miss more time?

ESPN's Adam Schefter reports that the 49ers previously weren't "overly concerned" about McCaffrey's status and initially expected him to play Monday. When he went in for treatment Monday, his calf "still was tight," per the report. Schefter reports that the injury could potentially sideline McCaffrey for next week's game against the Minnesota Vikings.

McCaffrey was initially listed as questionable for Monday's game on San Francisco's injury report released Saturday. Hufanaga was previously considered doubtful.

News of McCaffrey being sidelined comes a surprise after McCaffrey and head coach Kyle Shanahan reassured fans and media repeatedly throughout the preseason that he was on track to be ready to play in Week 1. McCaffrey initially suffered the calf injury in August early in training camp.

McCaffrey said Aug. 9 that his absence from practice was considered "cautionary" and that if the 49ers had a game that day, he'd be ready.

Shanahan has said throughout the preseason that he expects McCaffrey to play in Week 1. McCaffrey returned to practice for the first time last Tuesday, putting him on track to play Monday night.

He was then listed as a limited participant in Thursday's practice with an Achilles/calf designation prior to landing a questionable tag on Saturday. Shanahan told reporters Thursday that the Achilles designation was nothing new and that it was connected to his calf injury in training camp.

McCaffrey was seen running light drills during Thursday's practice.

McCaffrey is a three-time All-Pro. He led the league in rushing with 1,459 rushing yards and 2,023 yards from scrimmage in 2023. He tied for the NFL lead in touchdowns (21) with Dolphins running back Raheem Mostert. He was named the NFL's Offensive Player of the Year.

The 49ers enter the season on the heels of a Super Bowl appearance and are on the short list of favorites to advance to the Super Bowl again out of the NFC. McCaffrey, if healthy, is a big part of San Francisco's success and projections to compete again in 2024.