Andrew Bogut suffered a season-threatening broken leg on his Cleveland debut as the Cavaliers slumped to a 106-98 defeat against the Miami Heat on Monday.
Bogut, who only joined Cleveland as a free agent last Thursday, limped out of the action just 58 seconds into his debut at the Quicken Loans Arena following a collision with forward Okaro White.
The 32-year-old Australian star was helped to the locker room by his teammates and took no further part in the game.
Test results later revealed a fractured tibia, an injury which immediately placed a question mark against his availability for the rest of the season.
Cavaliers star LeBron James said he had guessed the seriousness of the injury after hearing a "crack".
"I heard a break," James told reporters. "As soon as the collision happened, I heard a break. When I went over to him and he said it, I already knew, I heard it crack."
The injury is another blow to the Cavaliers, who had already lost Kevin Love and J.R Smith to injuries.
Bogut's arrival had been seen as giving the Cavaliers' roster a key inside player with championship experience.
Bogut, a three-time Olympian with Australia, had helped the Golden State Warriors beat the Cavaliers in the 2015 NBA Finals.
"How would you think his spirit's like? He played 58 seconds," James said when asked about Bogut's mood. "And have an injury like that to take you out for the rest of the season, possibly, and you really, there's not much you can say," added James, who finished with 30 points.
With Bogut missing on Monday, Eastern Conference leaders Cleveland were on the wrong end of a determined Miami performance.
Former Cleveland player Dion Waiters scored 29 points against his former club to lead the Heat to victory.
Waiters made 12 of 24 from the field and capped his display by banking in a three-pointer as the seconds ran down to stymie a late comeback by the Cavs.
Waiters later admitted he had felt "good" scoring on his return to Cleveland.
"But the point is to get a win. That's the biggest thing," he said. "Especially against the champs. You always want to test yourself to see where you're at. That's a helluva team over there."
Waiters was ably supported by Goran Dragic with 21 points while Hassan Whiteside scored a useful 13 points with 11 rebounds.
Wayne Ellington impressed with an 18-point cameo from the bench.
The bulk of Cleveland's points came through James and Kyrie Irving. Irving finished with 32 points while James also had 17 rebounds as Cleveland attempted to reel in a 20-point deficit in the fourth quarter.