NEW YORK (AFP) - Boston Celtics forward Gordon Hayward vowed he "will be all right" in a video message on Wednesday (Oct 18) after a gruesome left leg injury from which he is expected to make a full recovery.

He appeared in a video message from his hospital bed before the Celtics' National Basketball Association (NBA) home opener against Milwaukee just a night after suffering the injury in a 102-99 loss at Cleveland.

"I'm going to be all right," he said in a video shown on the arena scoreboard. "It's hurting me that I can't be there for the home opener.

"I want nothing more than to be with my teammates and walk out on that floor tonight. But I'll be supporting you guys from here and wishing you the best of luck."

The Celtics fell 100-108 to the Bucks.

Hayward was flown back to Boston and taken to New England Baptist Hospital, where doctors diagnosed Hayward with a dislocated left ankle and fractured left tibia.

Celtics coach Brad Stevens said Hayward is expected to fully recover but would not estimate a timetable for when he might return until after surgery, which ESPN reported would be conducted on Wednesday night.

Stevens visited Hayward on Wednesday morning and spoke with him about the difficult recovery and rehabilitation period to come.

"He's feeling down," Stevens said. "Obviously there's a physical pain to it, but I think it's doubled by the emotional pain in that he put a lot of effort into trying to start his career out well in Boston."

Former Utah Jazz star Hayward, 27, signed a four-year deal worth US$128 million (S$173.9 million) with the Celtics in the offseason, expected to team with guard Kyrie Irving and big man Al Horford as an All-Star trio to make the Celtics title contenders.

But he lasted barely five minutes into the opener before making an awkward landing while attempting an alley-oop basket off a pass from Irving and his foot twisted at a horrific angle.

Players from both teams were stunned as medical staff rushed onto the court to treat him.

"This is a setback," Stevens said. "But we're expecting a full recovery. We know there will be a lot of tough days ahead on that recovery, but at the same time, I think hopefully he'll improve day-to-day."

He hopes playing well for Hayward can become a motivating factor for a young squad.

"They do want to play well for Gordon. I think the biggest thing is they really care about Gordon," he said. "He has made a big impact on them.

"Certainly you miss that and that camaraderie, but one of the tasks that we have now is to pick up steam for him."