EL SEGUNDO, Calif. — Rookie Kaelon Black looked powerful in his return to practice Tuesday, and another prominent San Francisco 49ers running back appears poised to return soon, too.

Following a fightless joint session with the Los Angeles Chargers, head coach Kyle Shanahan shot down a Monday report that Christian McCaffrey’s recent absence due to “tightness” might be tied to him wanting a reworked contract.

“People make a lot of assumptions, and that would be one that they’re wrong on,” the coach said.

Instead, he said McCaffrey would probably be back on the field already if the 49ers were getting ready for a regular-season game.

“If we were in a game week, I think he would have (practiced) today,” he said.

McCaffrey was observed working out on the Chargers’ practice field before the scrimmage began. He will certainly be held out of Thursday’s preseason game in Los Angeles. The team’s next practice after that is Saturday.

With McCaffrey watching from the sideline, the 49ers’ top runner Tuesday was Black, who’d missed the previous two weeks with an adductor (inner thigh) injury. The third-round pick certainly didn’t look rusty, taking an early carry to the left for 50 yards and showing violence and strength on several ensuing runs. Black also had a catch at the goal line in a red zone drill.

The video below shows Black’s longest run of the day. Chargers linebacker Denzel Perryman (No. 6) might have gotten him for a short gain, but Black seemed to think he would have broken the tackle.

“I thought he looked good hitting the hole and running hard,” quarterback Brock Purdy said. “You could tell there was a different level of intensity when he touched the ball. I’m excited to see what he does in live action (Thursday) with breaking tackles, hitting the gap and stuff like that. But I thought from the jump KB came out running pretty hard. So I was excited to see him back.”

The 49ers cut one of their backup tailbacks, Khalil Herbert, on Monday. That means the running backs  Thursday will likely be Black, Patrick Taylor Jr., Sincere McCormick and Zamir White. Jordan James (rib) and Isaac Guerendo (pectoral) continue to work their way back from injuries.

The tone of Tuesday’s session was decidedly different than last week’s against the Tennessee Titans in Santa Clara. That practice had to be halted three times in the first six snaps to break up scuffles between the 49ers’ defense and Titans’ offense.

Shanahan was asked whether he said something to his squad before they faced the Chargers.

“Nah, their head coach (Jim Harbaugh) had more discipline than Tennessee’s (Robert Saleh, the former 49ers defensive coordinator),” he quipped. “No, I’m just joking. A few things happened early in the Titans practice, and things just escalated throughout the rest of the day. I wasn’t on both sides (of the field Tuesday). But nothing happened early, and usually when nothing happens early, nothing happens late.”

Odds and ends

• If last week’s session with the Titans was a win for the 49ers, Tuesday’s was a defeat. The offense got off to a crisp start but began to falter midway through the session. Purdy finished the outing 15 of 30 against Derwin James and the Chargers’ first-string defense. Mac Jones was a bit more efficient with the second stringers, finishing 14 of 24.

“Honestly, I don’t think it was our best day — fundamentals and stuff,” Purdy said. “We were just a little off and whatnot. I feel like we could have come out with a little more chip on our shoulder.”

Purdy threw a touchdown to De’Zhaun Stribling during the red zone period but also had an interception when he forced a tight-window throw to tight end Luke Farrell and the ball got batted in the air. Purdy said it was a throw he might not attempt in a game.

“I wanted to try putting a tight ball onto Luke, and it was good coverage on the backside by the safety,” Purdy said. “He poked his hand out and popped the ball up. That’s practice. But I think it’s (worth) it to see if I can get it done or not.”

• Stribling and Trenton Irwin were the 49ers’ most active receivers. A few plays after his touchdown from Purdy (shown below), Stribling snagged a contested throw from Jones in the back corner of the end zone.

As he usually is when it comes to rookie receivers, Shanahan was stingy with his praise.

“Those were two good plays,” he said. “I think he had a couple rough ones too, so I’ll hold my opinion until I really see the tape. But he’s competing every day and getting better.”

• Veteran receiver Mike Evans left practice three quarters of the way in with what Shanahan described as “tightness.” Evans recently returned to practice after sitting out with a quadriceps strain.

“They just said he had some tightness, so we were just being smart taking him out,” Shanahan said. “I don’t think it’s anything worse, so we’ll see when we get in (the locker room), but nothing that I’m worried about right now.”

Receiver Demarcus Robinson was back after missing Sunday’s session, although he didn’t look like he was at full speed. Purdy seemed to have him on a deep throw down the middle of the field, but Robinson appeared dead-legged as the ball sailed beyond him.

“I know we’ve had some grinders and some practices the last couple of days,” Purdy said. “I don’t know if that had any effect or whatever on them today, but it was one day at practice, and they’re going to bounce back. We’re all going to be good.”

• Shanahan said defensive end Nick Bosa, who hasn’t practiced since Aug. 3 due to tendinitis in his surgically repaired knee, is on a similar trajectory to McCaffrey.

“He’s making a lot of progress,” Shanahan said. “He has a lot less irritation, soreness and tendinitis, whatever you want to call it, than he had last week. So we think he’s going in the right direction, and we see him similar to Christian.”

Shanahan said defensive end Mykel Williams, who tore his ACL six weeks after Bosa, was a “long shot” to play in Week 1.

“We haven’t ruled it out yet,” he said. “But he’s progressing very well.”

• Unlike in the preseason opener against the Titans, Shanahan said “a number” of starters would play Thursday against the Chargers. That group might include Purdy.

“I haven’t told him yet, but there’s a good chance,” Shanahan said.

• Rookie Carver Willis took all the first-team repetitions at left guard and will likely get a lot of snaps there Thursday. Robert Jones filled in at right guard for Dominick Puni, who is out with a concussion.

Several 49ers linemen have dealt with concussions in camp despite wearing Guardian Caps. The list includes Puni, Brett Toth and Willis on offense, and defensive linemen CJ West and Titus Leo, who suffered concussions on back-to-back plays Sunday. Linebacker Luke Gifford suffered a concussion in the spring.

“It just shows you, those only do so much,” Shanahan said of the Guardian Caps. “My favorite thing about those is the quarterbacks don’t break their hand as much (when they hit) the top of them. But regardless of what you’re wearing, if you get hit the right way, it’s not enough.”

• Asked if there were any specific 49ers players he was eager to see Tuesday, Harbaugh, speaking before the practice, mentioned one right away: “I want to meet Brock Purdy. Hopefully, Kyle introduces him to me.”

What does he admire about Purdy?

“How good he is — the timing, the decision-making, the accuracy,” Harbaugh said. “Just like … how cool he is, how cool he plays.”