Boston Celtics forward Gordon Hayward fractured his ankle in a heavy fall during their NBA season opener against Cleveland Cavaliers.
Hayward collided with LeBron James in mid-air during the first quarter and landed awkwardly, with his left ankle turning at an angle.
Both sets of players were visibly upset by the injury to the 27-year-old before the Cavaliers went on to win 102-99.
Hayward joined the Celtics in July in a deal worth $128m (£97m).
Celtics head coach Brad Stevens said. “Hopefully we get a full recovery and it’s a tough deal but I guess that’s part of it, the risk of injury. I really feel for him.”
Celtics’ new signing Kyrie Irving was booed during the game on his return to Cleveland, after he asked to leave the Cavaliers in the summer.
Elsewhere, defending champions Golden State Warriors lost 122-121 to Houston Rockets, with James Harden top-scoring with 27 points.
The Warriors thought they had won it with the final shot of the match, but replays showed the ball was still in Kevin Durant’s hand when the buzzer sounded.