SANTA CLARA >> It wasn’t much as practices go, but Monday’s session was enough to get the 49ers excited for what is to come with running back Christian McCaffrey.

Left tackle Trent Williams felt energized at the presence of “two-three,” referring to last year’s top offensive player by number. Quarterback Brock Purdy, in an informal chat with a few reporters, split into a wide smile as he described reaching for a handoff to the turbo-charged McCaffrey.

With the media window being less than five minutes during warmups, there wasn’t time for anything but a glimpse of McCaffery in uniform after missing the first eight games of the season with Achilles tendinitis that resulted in being placed on injured reserve in Week 2.

“You could feel it, just being able to see him out there,” rookie running back Isaac Guerendo said. “It’s a different type of feeling so I’m real excited for him.”

McCaffrey humorously eschewed a reporter’s “hello,” labeling it as a “gateway” to a group interview that will take place later in the week. Coach Kyle Shanahan isn’t available for interviews until today.Now comes the hard part for Shanahan and the coaching staff -- determining when to activate McCaffrey and then deciding how much he’ll play at the outset. The 49ers started a 21-day window Monday with McCaffrey’s first practice.

It could happen as soon as Sunday when the 49ers visit the Tampa Bay Buccaneers. It has been framed that way in national media reports, although general manager John Lynch stopped short of declaring it a certainty.

“Does that mean playing versus Tampa? No,” Lynch said in a recent 49ers-produced “Game Plan” interview with play-by-play announcer Greg Papa. “We’ll see where that goes.”

If McCaffrey is making the call, where it will go is straight into the starting lineup and the end zone. The running back’s impatience with his condition necessitated putting him on inured reserve, and the ensuing weeks included a trip to Germany for treatment.

On two occasions Shanahan has said, “We have to protect Christian from himself.” The first time was before McCaffery was injured and the question was about spelling the running back more judiciously to keep him fresh and healthy.

The second time was when he went on injured reserve, which immediately reduced the stress level of everyone involved and prevented McCaffrey from approaching his rehab as if it were a commando raid rather than a condition to be taken slowly, surely and seriously in hopes of getting him back for November and beyond.

It used to be that Shanahan was a big believer in rotating running backs. He never had a 1,000-yard runner with the 49ers in his first seven seasons. Only Carlos Hyde, in Shanahan’s first year in 2017, played more than 70 percent of the snaps.

The highest percentage since then was Elijah Mitchell, who got 64 percent of the snaps in 2021. Then came Oct. 20, 2022 when McCaffrey arrived from Carolina for four draft picks. McCaffrey instantly became Shanahan’s favorite toy.

Over 10 starts after his arrival, McCaffrey played 72.5 percent of all snaps and 77.4 in the playoffs. Last season, McCaffrey played a league-high 81 percent of all snaps in 16 starts and then 94.6 percent in taut playoff games against Green Bay, Detroit and Kansas City.

The only running back over 70 percent this year among the NFL rushing leaders is Philadelphia’s Saquon Barkley at 75 percent. Jordan Mason, the 49ers’ leading rusher with 685 yards, is at 63 percent.

Coincidence or not, McCaffrey’s 2023 workload that earned him a two-year contract extension has been followed by Achilles tendinitis. McCaffrey’s father Ed told the Ross Tucker Podcast last month that the condition in both legs was the result of overtraining.

Ideally, McCaffrey would help the 49ers improve their 48 percent rate of scoring touchdowns in the red zone.

It’s within Shanahan’s power as a play-caller and designer to ease McCaffrey’s workload in between the tackles while at the same time keeping him on the field as potential receiver, either split wide, in the slot or in motion.

That’s the point Shanahan was trying to make in June, although he expected a competitor’s resistance from McCaffrey.

“You’d like to take some of that off him and give it to the other guys,” Shanahan said.

Getting too greedy could end up with last year’s NFL Offensive Player of the Year back on the sidelines with the season in the balance, and it’s unlikely there would be time for another trip to Germany before the 49ers discover if they’re a playoff team or not.