What's the 49ers' plan if Christian McCaffrey can't play vs. Seahawks?

The San Francisco 49ers officially listed star running back Christian McCaffrey as "questionable" for Sunday's regular-season opener against the Seattle Seahawks at Lumen Field. If McCaffrey is unable to take the field, recently acquired running back Brian Robinson Jr. could be in line for the start.

Robinson, who joined the team via a trade with the Washington Commanders just before San Francisco's final preseason game, has been working quickly to absorb head coach Kyle Shanahan's offensive system.

"He's trying to learn it all," Shanahan said on Friday. "I mean, he's working his tail off doing it, studying, but he's been through three practices, so it's definitely not there yet. He'll get better throughout the year, but he's had a real good week."

The 49ers have Robinson listed as RB2 on the depth chart. Behind him, the team has Isaac Guerendo and rookie Jordan James on the active roster, although James is "doubtful" for Sunday due to a finger injury. San Francisco also has former Las Vegas Raiders running back Sincere McCormick on the practice squad.

Shanahan emphasized that Robinson is prepared to handle Sunday's game plan despite his short time in the system.

"Brian knows the game plan," Shanahan said. "You got it in this week. You don't have to know an entire offense. You've got to know what the plan is this week. And he's repped at it, so that's the situation. We're good to go with it, he's ready for it, and I know Isaac will be also."

The head coach also expressed confidence in Guerendo's progress since entering the NFL last year, believing the young back is ready to contribute if called upon.

"Isaac's a real smart kid, does everything well," Shanahan said. "Battled a number of injuries last year. Battled one in training camp, too. But I think he's gotten better and better since he's been here.

"Everyone will always be further along if they don't have setbacks. I think it was tough for him, missing a lot of training camp, but Isaac's doing good right now, and continuing to get back at it."

If McCaffrey can't go, the 49ers are expected to lean on a combination of Robinson and Guerendo, with James unlikely to play.