"He made a cut on air," head coach Kyle Shanahan told reporters via a conference call on Saturday. "It was the last play of practice. Made a cut on air. No one was around him. Just went down. It looked awkward."
The non-contact injury occurred shortly before the 49ers finalized their 53-man roster. The injury leaves the team with running backs Matt Breida, who is returning from a separated shoulder, Raheem Mostert, and newcomer Alfred Morris, who was signed on August 14.
Breida and Morris are now expected to share the workload on offense this season.
McKinnon, who was returning from a calf strain sustained on August 12, was expected to be the 49ers' featured back when they opened the season on September 9 against the Minnesota Vikings. It would have been a homecoming for the running back. The Vikings made McKinnon a third-round draft pick in 2014 and he played each of his four NFL seasons there.
McKinnon registered 1,918 career yards on 474 carries with seven touchdowns. He also added 94 receptions for 676 yards with four touchdown catches since 2016.
The 49ers also officially placed safety Marcell Harris on injured reserve. To take the two roster spots, the team signed defensive back Antone Exum Jr. and offensive lineman Matt Tobin.
San Francisco selected Harris out of Florida in the sixth-round of April's draft. He had a slow start with the Gators because he was recovering from a knee injury suffered in high school. Harris had a break-out season as a junior in 2016 when he registered 73 combined tackles, four for a loss, a forced fumble, a fumble recovery, a sack, and scored a touchdown on defense. He did not play during his senior season after suffering a torn Achilles last summer.
More San Francisco 49ers News
-
Dre Greenlaw opens up on 49ers return and reunion with Fred Warner
Dre Greenlaw is back with the San Francisco 49ers this offseason after spending the 2025 campaign with the Denver Broncos, and the veteran linebacker says the return has felt like coming home. Perhaps most importantly, Greenlaw is reunited with All-Pro linebacker Fred Warner,... -
Stats breakdown shows why 49ers' Kyle Shanahan and Brock Purdy remain elite
Every year, especially at draft time and heading into the season, fans are treated to a lot of potentially unfamiliar vocabulary. Three-technique or five-technique. This or that cornerback can or cannot flip his hips quickly. Statisticians have more categories than ever, even... -
49ers' Lynch and Shanahan detail how Brock Purdy won them over early in 2022
San Francisco 49ers general manager John Lynch and head coach Kyle Shanahan recently appeared on the Tom Tolbert Show. They revisited how quarterback Brock Purdy quickly earned the organization's trust during his rookie season in 2022. Lynch recalled an offseason practice in... -
49ers coach reveals what Kaelon Black must prove to earn a role in 2026
San Francisco 49ers running backs coach Bobby Turner was among the assistants who spoke with reporters on Tuesday, and much of the conversation centered on third-round draft pick Kaelon Black. The rookie entered the NFL with something to prove after many analysts labeled him a...