Yankees manager Aaron Boone did not reveal a status for King after the game, a 7-6 New York win, but had expressed his concern for him. On Saturday, before the Yankees took on the Orioles in the second game of the series, the team announced that the veteran had officially been placed on the 60-day IL.
"He's been one of the best pitchers in the league," Boone told reporters Friday. "I hope and pray the best for King."
The New York Post first reported on the severity of King's injury.
Right-hander Jameson Taillon said the mood among the Yankees was "somber" over King after the game.
"He's a hard worker. I know he'll get back here and get back to the same spot he was in," Taillon told reporters. "It's never easy seeing a guy walk off the field. You think about his girlfriend and family watching. That's not easy for anyone."
King, 27, had posted a career-best 2.29 ERA this season to go with a 6-3 record, one save and 16 holds in 34 appearances.
On Saturday, the Yankees also optioned outfielder Tim Locastro to Triple-A Scranton Wilkes-Barre.