The team physician for the NFL's Los Angeles Chargers accidentally punctured starting quarterback Tyrod Taylor's lung while trying to administer a pain-killing injection to his cracked ribs, the Chargers' head coach told ESPN on Wednesday.

The unusual incident happened shortly before Sunday's game between the Chargers and Kansas City Chiefs.

Chargers coach Anthony Lynn defended the physician and said he wasn't angry.

"It happens," said Lynn. "I can't go into details about it, but it was a complication with the shot. No one is perfect. It happens, but the doctor, I know he's a good man. It's just unfortunate."

Lynn said the injury is not career-threatening. The NFL Players Association is investigating the mishap.

"Our medical and legal team have been in touch with [Taylor] and his agent since Sunday, collecting facts," NFLPA assistant executive director of external affairs Georg Atallah tweeted Wednesday. "An investigation has been initiated."

Lynn announced that rookie quarterback Justin Herbert will start Sunday in the Chargers' game against the Carolina Panthers and that second-year quarterback Easton Stick would be the backup.

Lynn also noted that Taylor's availability will be evaluated on a week-to-week basis.

"He is in the building," Lynn said of Taylor. "He's doing fine. He's helping out with these young quarterbacks and helping get those guys ready to play."

Herbert, the team's No. 6 overall selection in the 2020 draft, filled in for Taylor, who had been listed as questionable with a chest injury before the start. The Chargers listed Taylor as "out" during the game.

The injection Taylor received is not entirely uncommon but carries some risk because the doctor injects the needle without seeing where it goes. However, it's very rare that a player suffers a punctured lung from the injection.

Taylor suffered two cracked ribs during the first drive of the Chargers' Week 1 win over the Cincinnati Bengals, but he played through the injury and didn't have an MRI until later that week. Taylor on Friday was added to the Chargers' injury report with a rib injury but was later removed from the report after fully participating in practice.

It had been planned for Taylor to take a pain-killing injection. After the physician punctured Taylor's lung, he went to a hospital due to breathing issues.