The team sent out a release late in the first quarter of Monday's game against Dallas that Hayward had successful surgery ''to repair a fourth metacarpal fracture in his left hand.''
''He was frustrated. He was down,'' coach Brad Stevens said at the team's morning shootaround. ''But this isn't like last time.''
Hayward, 29, missed all but five minutes of the 2017-18 season after breaking his leg in the first quarter of the opener against Cleveland.
Forward Jayson Tatum also said Hayward seemed frustrated after the latest setback.
''I feel bad for him. He was just getting back to being himself,'' Tatum said. ''It's a bummer.''
Hayward returned last season and played in 72 games, most of them off the bench, and averaged 11.5 points and 4.5 rebounds - far short of his numbers before the injury. He had been closer to his peak performance in the first seven games this season, averaging 19 points, four assists and a career-high seven rebounds before the latest injury.
''He'll be out a little bit and go from there, and he'll come back,'' Stevens said before the game. ''This is not a season-ending thing. There's a silver lining whenever you miss games is you're more fresh in the end. He's playing great, but there's other guys that are ready to step up and fill the void.''
His teammates know how well he was playing.
''The crazy thing is he was playing unbelievable,'' forward Enes Kanter said. ''I said in the beginning of the season, 'He's back, 100%. And he's going to shock the world.' He was shocking the world. Now he's got that injury. But I know he's going to come back and be amazing again.''
Kanter was cleared to return for Monday night's game against the Dallas Mavericks after missing seven games with a left knee contusion. Kanter said he was not aware of any limitations on his playing time.
''Let's see what happens tonight,'' he said. ''I've been like trying to get into game shape the last two weeks. We'll just see how it feels.''
AP Freelancer Ken Powtak contributed to this story.
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