Indiana Pacers star Paul George suffered a grisly lower right leg injury in a United States intra-squad scrimmage in preparation for the Basketball World Cup.
The injury was bad enough that the exhibition before fans in Las Vegas was halted and George was taken to hospital.
He later underwent successful surgery for a broken leg and is expected to remain in hospital for about three days. Doctors estimate a full recovery could take as much as 18 months.
He later tweeted his thanks for the outpouring of concern he received. "Thanks everybody for the love and support.. I'll be OK and be back better than ever!!!" he said.
Although he was upbeat, the reaction from those who saw the injury occur - either first-hand or via video replays - showed just how shocking it was.
"It was difficult to watch the injury that Paul George sustained tonight while representing his country," NBA commissioner Adam Silver said in a statement. "The thoughts and prayers of all of us at the NBA are with Paul and his family."
The Pacers small forward landed hard and his leg buckled horribly near the basket stanchion after he had fouled James Harden on a drive early in the fourth quarter.
Harden doubled over in shock upon seeing the injury to his US teammate and medical personnel, US coach Mike Krzyzewski and members of George's family attending the game moved to comfort the stricken player.
After George had been taken from the court with his leg in a splint, Krzyzewski announced that the contest would be halted.
"With the serious injury that we had and the fact that we stopped playing for a long period of time, and out of respect for Paul and his family, the scrimmage is done," he told the crowd.
USA Basketball chairman Jerry Colangelo said the organisation's only concern at the moment was for the player.
"This is a very tough blow," a grim-faced Colangelo said. "It's a tough situation for our entire organisation, our coaches and players are very, very emotional."
Colangelo said decisions about the final US selection for the Basketball World Cup, to be held in Spain from August 30 to September 14, would take a back seat to making sure George was cared for properly.
"Our first concern, our primary concern, is Paul George," he said. "And so, as an organisation, we're just going to let a little bit of time go by here before we address rosters or any of that stuff. It seems unimportant."
George, 24, has been an All-Star each of the last two years. He averaged 21.7 points, 6.8 rebounds and 3.5 assists in 80 games last season for the Pacers, who lost to Miami in the Eastern Conference finals.