EL SEGUNDO >> Justin Herbert, the Chargers’ standout quarterback, will be sidelined from training camp for approximately the next two weeks after he was diagnosed with a plantar fascia injury in his right foot, the team announced Thursday. Doctors diagnosed the injury on Wednesday and recommended Herbert wear a walking boot.

The Chargers said in a news release that they expected Herbert would be sound enough to play in the regular-season opener against the Las Vegas Raiders on Sept. 8 at SoFi Stadium. Easton Stick took the bulk of the snaps Herbert would have taken as training camp continued Thursday.

“No update,” Chargers coach Jim Harbaugh said after practice when asked about Herbert’s condition.

Harbaugh also said he was “not qualified to know when it happened,” when asked if Herbert was injured during Wednesday’s practice or whether it was something that had been troubling him for days, weeks or months. “He was evaluated (Wednesday) night and diagnosed (Wednesday) night.”

Injuries to the plantar fascia, the connective tissue at the bottom of the foot that runs between the heel and the toes, are most commonly found among long-distance runners, ballet dancers and others who are on the feet for extended periods each day. The primary symptom is heel pain.

Surgery is generally not required except in extreme cases, but rest is the best cure for an ailment that often lingers for several weeks or more.

Herbert has had significant injuries in each of the past two seasons. He suffered fractured rib cartilage in Week 2 of the 2022 season during a game against the Kansas City Chiefs, but he did not miss a game despite the debilitating injury. Last season, he was sidelined by a broken index finger for the final four games.

Stick filled in for Herbert, making his first regular-season starts. He completed 63.8% of his passes in the Chargers’ losses to the Raiders, Buffalo Bills, Denver Broncos and the eventual Super Bowl champion Chiefs. He passed for 1,129 yards with three touchdowns and one interception.

Herbert has completed 66.6% of his passes for 17,223 yards with 114 touchdowns and 42 interceptions in 62 career games over his four seasons in the NFL. Last season, he completed 65.1% of his passes for 3,134 yards with 20 touchdowns and seven interceptions before he was hurt.

It was uncertain whether Herbert — who last summer agreed to a five-year, $262.5 million contract extension that briefly made him the highest-paid player in the NFL — would have played in any of the Chargers’ three upcoming exhibition games, including their preseason opener against the Seattle Seahawks on Aug. 10 at SoFi Stadium. It was expected that Stick, Max Duggan and Casey Bauman would quarterback the Chargers.

Duggan is a second-year pro who has yet to appear in a regular-season game. Bauman is an undrafted rookie from Augustana University in Sioux Falls, South Dakota.

“The preparation continues,” Harbaugh said when asked what impact Herbert’s injury and absence would have on training camp for a team with new wide receivers, tight ends and running backs on the roster. “Full steam ahead. The preparation, the work continues. He’s not on the field, in the practice, but still in the meeting room, still in the training environment. That chemistry, that rapport you build with those position players, his teammates, that continues.”

Stick had a mixed showing during Thursday’s practice, joining what appeared to be mostly members of the starting offense while facing what appeared to be the starting defense for the first time in eight camp sessions so far. He zipped a touchdown pass to a leaping Joshua Palmer during a 7-on-7 period for one highlight.

However, Stick, entering his sixth NFL season, had several misfires during other periods.

“He was the same as he was the day before,” Harbaugh said of Stick, who had been working exclusively with the second- and third-string offensive players, including backup center Brenden Jaimes until Thursday. “He attacks everything he does. The way he goes about his business is top-notch.”

Extra points

Rookie wide receiver Ladd McConkey didn’t participate in Thursday’s practice. Harbaugh indicated that McConkey was working through something, but didn’t elaborate. ... Edge rushers Joey Bosa and Khalil Mack and running back Kimani Vidal left the practice field accompanied by athletic trainers for the adjacent facility. Bosa and Mack each returned to practice. ... Offensive lineman Jordan McFadden continued to take a turn or two or three as a tight end.