By Matt Barrows, RJ Kraft and Jenna West

The San Francisco 49ers plan to place running backs Christian McCaffrey and Jordan Mason on injured reserve after suffering injuries in the team’s Week 13 loss to the Buffalo Bills.

McCaffrey suffered a PCL injury but will not need surgery, coach Kyle Shanahan said Monday. The injury is about a six-week recovery time, which sidelines the 2023 Offensive Player of the Year for the remainder of the regular season. Additionally, Mason suffered a high ankle injury in the loss and will be placed on IR. Both must miss a minimum of four games; the 49ers have just five games left this season.

These latest injuries mean the 49ers’ top three running backs from the start of the offseason — McCaffrey, Mason and Elijah Mitchell — are all on injured reserve. Rookie Isaac Guerendo is the only healthy running back, not including fullback Kyle Juszczyk, on the roster, though Patrick Taylor Jr. is on the team’s practice squad. The 49ers will have to go outside the building to sign at least one more back. Matt Breida, who played for the team from 2017 to ’19 and spent three weeks on the roster during training camp, would seem to be a potential option.

McCaffrey left Sunday night’s game early in the second quarter. Taking a carry on a first down play, McCaffrey took a few slow steps before sliding to a stop for a 5-yard loss. he left the field under his own power and went to the medical tent, then attempted to jog along the 49ers sideline before heading to the locker room.

Sunday was just McCaffrey’s fourth game of the 2024 season. He returned in early November after missing most of training camp and the 49ers’ first eight games because of tendonitis in both Achilles. He had seven carries for 53 yards and two catches for 14 yards before exiting Sunday’s game. For the season, McCaffrey had 202 rushing yards along with 15 receptions for 146 receiving yards.

Mason was the team’s primary running back for the first two months of the season while McCaffrey was out with his initial injury. The third-year back leads the team in rushing with 789 yards and has three touchdowns.

Guerendo, a fourth-round pick out of Louisville, has shown promise while filling in for Mason when he was hurt against the Seattle Seahawks (Week 6) and the Dallas Cowboys (Week 8). He has 246 rushing yards and two touchdowns on the season.

Additionally, defensive tackle Kevin Givens suffered a torn pec in Sunday night’s loss. He is out for the season and will also be placed on injured reserve.

The 49ers (5-7) have lost three in a row and sit two games behind the Seattle Seahawks in the NFC West.

What do the 49ers have in Guerendo?

The injuries to McCaffrey and Mason mean Guerendo suddenly will become the 49ers’ lead tailback, and it likely also will prompt the 49ers to promote Taylor from the practice squad. Guerendo seemed to be starting to find his stride when McCaffrey returned from his Achilles injury and immediately received nearly all of the tailback snaps.

Now, Guerendo will get an opportunity to resume his NFL education. He’s shown flashes of potential, including on Sunday when he had a 15-yard touchdown against the Bills. But he’s also fumbled twice on kickoffs (losing one) this season and it’s not quite clear whether he’s fully shaken the injury bug that plagued him in college.

In short, Guerendo — and the 49ers — will benefit from him getting more snaps. It will better prepare him for the 2025 season and ought to give the team a better idea on how to approach Mason’s situation — he’ll be a restricted free agent in March — when the season is over. — Matt Barrows, 49ers beat writer

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(Photo: Timothy T Ludwig / Getty Images)