The 49ers need to add to their running backs room after losing both Christian McCaffrey and Jordan Mason to injuries in their 35-10 loss to the Buffalo Bills.

Both running backs will be placed on injured reserve, meaning they will miss at least four games beginning in Week 14. McCaffrey suffered a PCL injury that coach Kyle Shanahan estimates will require at least six weeks of recovery, while Mason suffered a high ankle sprain.

Speaking with Mason after the game, the third-year player did not appear to be dealing with an ankle injury, but was seen in the locker room with a bandage on his right arm before the team flew back to the Bay Area.

The 49ers will now rely on rookie Isaac Guerendo, who appeared in 12 games this season and recorded 42 carries for 236 yards and two touchdowns. Fourth-year running back Patrick Taylor will also be in the mix.

“We obviously have Guerendo who will be up,” Shanahan said via conference call Monday. “We have Patrick here who is on our training team and he will definitely be strengthened now.

“(Taylor) was on our roster at the beginning of the year before Christian came back. We will most likely have to look for another one.”

Guerendo was the 49ers’ fourth-round pick (No. 129) in the 2024 NFL Draft and is known for his 40-yard dash speed of 4.33. Taylor is an undrafted free agent, a burly, 6-foot-1, 220-pound defensive back who spent his first three NFL seasons with the Green Bay Packers.

One free agent the 49ers could consider is Jerick McKinnon, who signed with the 49ers in 2018 before suffering a torn ACL during training camp. The Georgia Southern product knows the system well and was able to integrate quickly.

Matt Brieda is also a free agent and is familiar with the 49ers’ offense, having spent his first three NFL seasons in the Bay Area before playing with the Miami Dolphins, Buffalo Bills and New York Giants. Royce Freeman, a member of the Los Angeles Rams in 2023, could also be a candidate.

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