SANTA CLARA, Calif. -- After returning to practice last week following a hamstring injury, San Francisco 49ers running back Elijah Mitchell's comeback hit a significant roadblock on Tuesday.
In a bit of a surprise move, the Niners placed Mitchell on injured reserve on Tuesday afternoon and did not use one of their designations for Mitchell to return, which rules him out for the season.
A source told ESPN on Tuesday evening that Mitchell suffered another, more severe hamstring injury this week. That injury is believed to have happened during the team's practice on Monday when Mitchell was in uniform and participated in individual drills but did not take part in any of the team periods.
Mitchell's injury is the latest in a series of ailments that have prevented him from gaining traction as a top option in San Francisco's run game and could mean he has played in his final game for the team.
This is the fourth and final year on Mitchell's rookie contract, making him an unrestricted free agent after the season. In his three previous campaigns, Mitchell has appeared in just 27 games with 12 starts because of various injuries, including rib, finger, knee and shoulder issues.
As a rookie in 2021, Mitchell burst onto the scene by rushing for 963 yards and five touchdowns in 11 games after replacing an injured Raheem Mostert as the starter. But Mitchell appeared in just five games in 2022 when the Niners traded for Christian McCaffrey, who has taken the bulk of the running back snaps since his arrival in October of that year.
In this year's training camp, Mitchell was in a competition with Jordan Mason to be McCaffrey's primary backup before hurting his hamstring the first time in early August.
In his two previous seasons, Mason averaged 5.6 yards per attempt on 83 carries with four touchdowns. Mason's improved versatility had already put him in position to replace Mitchell as McCaffrey's primary backup, but Mitchell's inability to stay on the field made that competition moot.
"He's been such a good runner since he's gotten here," Niners coach Kyle Shanahan said of Mason after Friday's preseason finale against the Las Vegas Raiders. "I think his stamina has gotten better. I think his all-around play, especially on special teams too, has gotten a lot better.
"He's been running the ball well for a while. He's solid in the pass game, as well."
Mason has served as the 49ers' top back for most of training camp as McCaffrey has been dealing with a calf injury. In addition to McCaffrey and Mason, the Niners kept two other running backs -- Patrick Taylor Jr. and rookie Isaac Guerendo -- on their initial 53-man roster.