Bayern Munich on Friday threatened Canada Soccer with legal action after defender Alphonso Davies returned from the March international break with a torn anterior cruciate ligament.
In an interview with German tabloid Bild published Friday, Bayern CEO Jan-Christian Dreesen said the club wanted a "complete clarification of the events", accusing Canada Soccer of "gross negligence" and saying "we reserve the right to take legal action."
Davies, the Canada captain, went off injured 12 minutes into a third-place Concacaf Nations League play-off with the United States on Sunday, which the Canadians won 2-1.
Canada Soccer initially gave the 24-year-old the all clear, but an examination in Munich revealed he had torn his ACL, ruling Davies out for at least six months.
"Sending an obviously injured player with a damaged knee on a twelve-hour intercontinental flight without a thorough medical assessment is, in our view, grossly negligent and a clear breach of medical duty of care," Dreesen said, saying the match had "little sporting significance".
"Phonzy (Davies) is not at fault, he's the captain and he wants to take responsibility... Canada as host nation of the 2026 World Cup has already qualified, you can't take risks with a player like him."
In a press conference on Friday, a visibly frustrated Bayern sporting director Christoph Freund told reporters Canada Soccer's decision was "borderline and negligent", adding "the way things went down was incorrect."
"We are the employer and also pay the players, so we will investigate."
Bayern, who are currently missing captain and goalkeeper Manuel Neuer, also lost centre-back Dayot Upamecano to a long-term leg injury in the international break.
Bayern confirmed Upamecano's injury this week and German media suggested he may be out until the end of the season.
Bayern sit six points clear of defending champions Bayer Leverkusen in the league and face St Pauli at home on Sunday.
In the Champions League, Bayern face Inter Milan in the quarterfinals, with this season's final to take place in Munich.