CLEVELAND — Celtics forward Gordon Hayward was stretchered off the floor in Cleveland after suffering a horrific-looking ankle injury a little more than five minutes into his Boston debut Tuesday night.

The team later announced that Hayward fractured his left ankle. He will be flown back to Boston later Tuesday night.

Hayward’s left leg bent awkwardly after he went up for an alley-oop pass, collided with LeBron James and collapsed under the basket with 6 minutes, 45 seconds left in the first quarter. Teammates and Cavaliers players, including James, rushed to check on him as he was stretchered from the court.

Hayward’s left ankle turned at such an odd angle that teammates stood in shock as he motioned for help from the sideline.

Cavaliers guard Dwyane Wade knelt with his hand on his head nearby as team doctors attended to Hayward. Shell-shocked Celtics players huddled, with Kyrie Irving burying his head in the chests of teammates Marcus Smart and Jayson Tatum.

Fans gave Hayward a standing ovation as he was taken from the court with his entire left leg immobilized in an air cast. He was immediately taken to the Cavaliers’ locker room for more evaluation.

Numerous doctors and Cavaliers and Celtics officials were with Hayward in the Cleveland locker room, where he received X-rays that confirmed the broken ankle. Many were ashen as they left, including Cavaliers general manager Koby Altman.

Isaiah Thomas, who recruited Hayward to Boston this summer, was in the locker room with him for an extended period before returning to the bench.

Cavaliers owner Dan Gilbert, who recruited Hayward to Cleveland as a free agent in 2014, also visited him.

Players across the league immediately reacted on social media to the injury, including Paul George, who broke his leg in a gruesome injury in 2014.

“It was terrifying,” said Golden State Warriors coach Steve Kerr, whose team was readying for its season opener against the Houston Rockets. “The whole coaches’ office was just devastated watching it. It just shows the fragile nature of what we do.”

Hayward signed a four-year, $128 million contract with the Celtics in July, making him the first of two All-Stars that they acquired this summer. Boston later picked up Irving in a trade with the Cavs.

Hayward’s arrival in Boston reunited him with his former Butler coach Brad Stevens.

The Celtics lost Tuesday night’s game 102-99.

Information from ESPN’s Brian Windhorst was used in this report.