The injury that made Chargers quarterback Tyrod Taylor a late scratch on Sunday was a punctured lung inadvertently caused by a team doctor administering an injection, ESPN reported Wednesday.
The US sports website cited unnamed team and league sources as saying the doctor was giving a pain-killing injection for Taylor's cracked ribs when the injury occurred.
Taylor was a last-minute scratch from the Chargers' game against the Super Bowl champion Kansas City Chiefs, and required a brief hospital visit for what the team later described as complications from an injection.
NFL Network reported Wednesday that Taylor appears unlikely to play on Sunday when the Chargers host the Carolina Panthers.
The NFL Players Association has launched an investigation in the wake of the ESPN report, NFLPA spokesman George Atallah said in a statement posted on Twitter.
Atallah said the union's "medical and legal team have been in touch with Tyrod and his agent since Sunday collecting facts."
In Taylor's absence, rookie Justin Herbert led the Chargers offense against the Chiefs, delivering two touchdowns and more than 300 passing yards.
Despite his encouraging performance in the overtime defeat, Chargers coach Anthony Lynn said Taylor would return to the starting job when he is fit.