The backfield distribution for the 49ers on Sunday was… worrisome. Christian McCaffrey played all 57 snaps, making him the only player besides Brock Purdy and the offensive line to play 100 percent of the offensive snaps.

That was not by design.

Kyle Shanahan was asked Monday whether he and his staff need to do a better job of mixing in other running backs to ensure McCaffrey stays healthy all season.

He didn’t deflect from the question.

“Yeah, we definitely got to get Elijah [Mitchell] in there more and do better with our rotation than we did yesterday,” Shanahan said. “That wasn’t the plan going in. It just ended up that way and I got to make sure that doesn’t happen.”

While Shanahan isn’t in charge of substitutions, he obviously has say in personnel. He took blame for Mitchell failing to even take one snap.

“Usually calling plays, you can ask for guys specifically on certain plays as a play caller,” Shanahan said. “But no, you’re not keeping guys fresh and rotating and doing stuff like that. Position coaches do that. But for him not to get in, I definitely should have noticed and asked for him.”

The 49ers have legendary running backs coach Bobby Turner in charge of that group, along with Anthony Lynn, who’s assistant head coach/running backs coach. It’s a pair of highly respected veteran coaches that you would expect to have a better rotation going forward.

McCaffrey was stellar, rushing for 116 yards and a touchdown on 20 carries, and catching three passes for 19 yards.

In the season opener, Mitchell took 10 snaps (15 percent), compared to 58 for McCaffrey (85 percent). Jordan Mason has been the team’s third back and exclusively used on special teams, while Ty Davis-Price has been a healthy scratch thus far.

The 115 snaps for McCaffrey have him on pace for 977.5 snaps this season, before the playoffs.

That would be the second most in his career, ahead of 966 snaps in his 2018 sophomore campaign in Carolina, but behind his 1,039 snaps his third year.

He took 777 snaps in the regular season last year and another 137 in the postseason (914 total). Given the 49ers’ playoff expectations, the current workload would set him him for a career high over the course of the season.

Those two heavy workload years seemed to take a toll on McCaffrey. After that 1K snap season, he played just 10 games over the next two years, before last season’s resurgence.

The 49ers are clearly not the same team without him, and with a short week coming up, you’d imagine that they’ll mix in Elijah Mitchell for his heaviest workload of the season.