49ers injuries (including to Ricky Pearsall) mounting again, while Brock Purdy rebounds

SANTA CLARA, Calif. — General manager John Lynch said the San Francisco 49ers looked into the electrical substation next door and were assured everybody is safe. That was after a seemingly nonstop sequence of injuries last season.

The 49ers then put a lot more money — in terms of equipment and staff — toward bolstering the training and health of their players. They changed the training camp practice schedule, adding a jog-through session every fifth day to ease the wear and tear on players who are ramping up for the regular season.

And yet …

Three practices in, the 49ers are losing players at an alarming rate, including receiver Ricky Pearsall, who missed Wednesday’s practice with some swelling in his right knee. It is the same knee in which Pearsall injured his PCL in Week 4 last season, forcing him to miss six games and at times bothering him after he returned.

The 49ers are concerned. Pearsall was set to start opposite newcomer Mike Evans but might now be looking at surgery. Assistant head coach Chris Foerster — who is standing in for Kyle Shanahan while the head coach recovers from a concussion and other injuries suffered in a recent car accident — next talks to reporters on Friday. Thursday is a much-needed rest day.

Second-year running back Jordan James was also out Wednesday after suffering a rib fracture in Monday’s practice. He had looked crisp at the start of camp, and observers were looking forward to a fierce battle between James and rookie Kaelon Black for the backup running back job behind Christian McCaffrey.

Safety Malik Mustapha is out with a strained hamstring. The 49ers already had injuries to receiver Christian Kirk (calf), offensive tackle Vederian Lowe (ankle) and rookie defensive tackle Gracen Halton (knee) at the first practice on Sunday.

If you’re going to try and spin some positive out of this, it means more reps for Black and impressive rookie receiver De’Zhaun Stribling, who caught everything and made it look easy again on Wednesday.

“Kaelon’s a pro, man,” McCaffrey said. “He knows how to work, he knows how to learn and … he’s explosive and sees the hole really well. … (Stribling) plays full speed, man. It’s another rookie who I think when you look at our whole rookie class, it’s just a lot of guys who put their head down and work. And that’s exactly what you want. That’s what our vets do, that’s what our young guys do.”

Brock Purdy’s revenge

Following a Monday practice in which aggressive defensive backs got their hands on a lot of passes, Brock Purdy and the other quarterbacks had a measure of revenge. Purdy was 14 of 18 during the team portion of practice, including on a crisp crossing-route throw to Demarcus Robinson that was just beyond the reach of linebacker Fred Warner.

Purdy also seemed on target on a deep ball to Mike Evans, but the receiver wasn’t able to bring in the pass.

Mac Jones started slowly, with cornerback Jack Jones — who’s gotten his hands on a lot of passes early in camp — outleaping Jacob Cowing on a 50-50 ball for an interception. Mac Jones improved throughout the session and finished 11 of 15.

Second-year player Kurtis Rourke was 5 of 5 with the third-team offense, including a good back-shoulder throw to Jordan Watkins at the sideline. Rourke and Adrian Martinez are competing to be the No. 3 quarterback this season.

“They’ve done a good job so far,” offensive coordinator Klay Kubiak said Wednesday. “To me, that’s going to emerge through the preseason games. That’s when those guys are going to get most of their reps, is in preseason. They’re going to play a lot. That battle, that competition will kind of play itself out, and whoever plays the best is probably going to end up winning that battle.

Odds and ends

• Rookie defensive end Romello Height, who was carted off the field Monday with cramps, was back on Wednesday with a new jersey. Height started camp in No. 94 and is now wearing No. 58.

The team also made some changes at his position, waiving William Bradley-King and Andrew Farmer II with injury designations and replacing them with Quinton Bell and K.J. Henry.

• Mustapha was working on a side field Wednesday after straining his hamstring earlier in the week. That will put a pause on his competition with Marque Sigle, who worked alongside Ji’Ayir Brown with the first-team defense. Siran Neal — who had a nice pass breakup — and Ashtyn Davis worked with the second unit.

• One of the standouts so far: Dre Greenlaw, who has been teaming with Warner to torment ball carriers and pass catchers in the middle of the field. Wednesday’s team session began with Greenlaw stripping McCaffrey of the ball and recovering the fumble.

• The 49ers were coming off a so-called “jog-through” session on Tuesday, which Kubiak said was added to the schedule this year so that the players don’t practice for three consecutive days in camp. The team has its first league-mandated players’ day off on Thursday.

Kubiak noted that veterans often didn’t practice on the third day of each practice segment anyway, which in the past has meant extra repetitions on those days for everyone else.

“The way we’re doing it now is everyone’s out there every day, and we don’t have to compensate for a lower number (of players) in a practice, which is where sometimes you might get an injury,” he said. “When you’re low on receivers, one day you’re low on linemen or something, guys have to take more reps. So we’re trying to avoid that as best we can by adding that jog-through day.”

Observers, of course, will note that the new system hasn’t helped the team avoid injuries to begin training camp. Two of the team’s top four receivers — Kirk and Pearsall — were injured during the first two sessions, as was No. 2 running back James. Three tryout receivers joined Wednesday’s practice: Alex Bachman, D’Wayne Eskridge and Trenton Irwin.