BOSTON Celtics star signing Gordon Hayward has suffered a horrific leg injury in his first game in green.

The small forward fell awkwardly after jumping high to reach for an alley oop pass from new teammate Kyrie Irving less than six minutes into the opening quarter of today's season-opener in Cleveland when tragedy struck.

He fell in a heap in the paint with his foot facing the wrong direction and was stretchered off with his left leg immobilized from foot to thigh, sitting up on the stretcher as he was carried off.

The Celtics announced shortly after the 27-year-old had suffered a fractured left ankle.

Hayward's injury completely changes the picture in the Eastern Conference, where the Celtics were expected to offer the biggest challenge to the Cavaliers' recent dominance.

After falling 4-1 to the Cavs in last season's Eastern Conference Finals, the Celtics added the Utah Jazz free agent and Cleveland point guard Irving in a bid to make it back to the finals for the first time since 2010.

The Celtics were leading 12-9 when Hayward went down but quickly fell behind as the Cavs closed the opening quarter on a 14-2 run. Cleveland led 54-38 at halftime but Boston surged back in the third to close to 72-71 with a quarter to go.

Cleveland star LeBron James, who had attempted to break up the play, and Celtic-turned-Cav Isaiah Thomas both went to the locker room where Hayward was being treated to offer their support, per ESPN's Brian Windhorst.

Paul George and Shaun Livingston, who both suffered similarly gruesome breaks, immediately tweeted their support.

George broke the tibia and fibula in his right leg while trying to block a shot during a scrimmage with the US men's national team in August, 2014. "The pain was tough," George said later. "As soon as the air hit my bone, where the open wound was, it just shot through my whole body. Everything just slowed down. Like, I could hear every individual in the arena talking."

Livingston dislocated his kneecap and tore the ACL and PCL in his left knee while playing for the LA Clippers against the Charlotte Bobcats in 2007.

Hayward's injury has rocked the entire league.

Hayward had spoken before the game about wanting to get a win for Irving in his return to Cleveland.

"Yeah, it's gonna be a fun atmosphere for sure," Hayward said, per Jay King of MassLive. "A huge game for Kyrie and I think one we're all looking to play our best for him. Not only for the team, but for him. We know it's a big game for him."

Kyrie Irving wasn’t the only player who couldn’t look.
Kyrie Irving wasn’t the only player who couldn’t look.

PHOTO GALLERY: Fast and furious night at Kingaroy Speedway

Premium Content PHOTO GALLERY: Fast and furious night at Kingaroy Speedway

DRIVER’S from around Queensland flocked to Kingaroy Speedway over the weekend for...

VIDEO: JT’s message of resilience to the South Burnett

Premium Content VIDEO: JT’s message of resilience to the South Burnett

JOHNATHAN Thurston shares a heartwarming message for South Burnett residents hit...

The real powerhouses behind Qld politics

Premium Content The real powerhouses behind Qld politics

Queensland’s election campaign is not all posing and promises,