LeBron James and Kyrie Irving said Tuesday that Gordon Hayward's sickening leg injury in his debut for the Celtics is among the worst they have ever seen. 

Hayward, 27, dislocated his left ankle and fractured his left tibia early in Boston's season-opening 102-99 loss to the Cavs.

The All-Star was making his bow for the Celtics after arriving from the Jazz amid much optimism but it ended it agony after he came down on his ankle as he jumped in an effort to catch a pass during the first quarter.

Celtics and Cavs players turned away in horror as Hayward grimaced in pain at Quicken Loans Arena, and fellow Celtics debutant Irving – facing his former team – was immediately reminded of Paul George's gruesome leg injury for Team USA in 2014.

"It's tough. I've seen a few injuries in my career and I've had a few," said Irving, who posted 22 points and 10 assists in Cleveland.

"Probably two of the worst ones I've been in the game watching - one was [Paul George] at USA and this one tonight. It's not a great sight to see but you gotta pick yourself up. Just keep on fighting, man.

"We understand that [Hayward], God-willing, will be fine, and we're going to continue to pray for him and be there for him as best we can."

Celtics head coach Brad Stevens said: "He's put in a lot of great work. And I thought he had his most comfortable week as far as feeling like he was going to play really well. But now we'll hopefully get a full recovery, right? And so it's a tough deal, but I guess that's part of it: the risk of injury. I really feel for him."

Added James: "I've seen a couple of injuries like that in my lifetime. I've seen Paul George when it happened to Paul. I was watching the game with Shaun Livingston when it happened when he was with the Los Angeles Clippers. I was watching NCAA basketball when Kevin Ware was at Louisville.

"Those are the injuries that you never seen coming and you never want to happen, no matter who it is, no matter what the stature, no matter how much competitive nature that you have. It's just very unfortunate."