Boston Celtics forward Jayson Tatum tore his right Achilles tendon in Game 4 of the Eastern Conference semifinals against the New York Knicks on Monday at Madison Square Garden. The Celtics, who are down 3-1 to the Knicks, announced on Tuesday that Tatum has already undergone surgery on his Achilles.

When Jayson Tatum toppled to the court, writhing in pain and grabbing at his right foot late in the Celtics’ Eastern Conference semifinals Game 4 loss to the New York Knicks, it looked like a potentially season-altering injury.