On Sunday, just days before their opening night matchup against the three-time defending Eastern Conference champions Cleveland Cavaliers, Gordon Hayward was asked about the start of the season. "I guess I'm just ready to get going," Hayward said. "Lots of things happened this summer, lot of buildup, I'm just ready to get to the games." In an offseason where it felt like every superstar switched jerseys, the Celtics stood out a particular intriguing team. After winning 53 games and advancing to the Eastern Conference Finals, the Celtics drafted Jayson Tatum, signed Hayward, traded for Kyrie Irving and returned just four players from last season's roster. They were ready to roll.

But on Tuesday, everything came crashing down. In the first quarter against the Cavs, Hayward went up to catch an alley-oop pass from Irving, collided with LeBron James and Jae Crowder in mid-air, and fractured his left ankle while landing awkwardly on the court. The Cavs bench reacted in horror as soon as they saw Hayward's fall, as did everyone else who saw the play unfold. A hush fell over Quicken Loans Arena, and after an extended period on the court with the Celtics medical staff attending to him, Hayward was placed on a stretcher and taken to the locker room for further examination.

Both LeBron and Isaiah Thomas visited Hayward in the locker room during the game to offer their support. Players from around the league reacted as well, including Paul George and Shaun Livingston. The game resumed, but it felt like an afterthought. The subplot of Irving to Cleveland didn't matter anymore. The Celtics erased an 18-point deficit and took a fourth quarter lead before LeBron (29 points, 16 rebounds, 9 assists) helped orchestrate a comeback, aided by a corner three from Kevin Love with less than a minute to go to seal a 102-99 victory. But no one really cared to analyze the game afterwards. All the focus was on Hayward.

"I've seen a couple injuries like that in my lifetime," LeBron said. "I've seen Paul George ... I was watching the game with Shaun Livingston when it happened when he was with the Clippers. I was watching NCAA basketball when Kevin Ware was at Louisville. Those are the injuries that you never see 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."

Jaylen Brown, who scored a team-high 25 points and will have to take on a much larger role on both ends of the floor, was as stunned as everyone else. "It's tough," Brown said. "Gordon is a leader of our team, and going into the season we leaned on him a lot." Reporters asked head coach Brad Stevens whether he had a message for his players to help them regroup after Hayward's injury. "I don't have any magic words for that," Stevens said. "I mean, you're all hurting for him. I'm not going to try and take the human element out of it."

Hayward will have surgery on Wednesday and will miss a significant period of time, possibly the rest of the season. Now the Celtics must scramble to adjust. The 27-year-old forward averaged 21.9 points last season in Utah, shooting 47.1 percent from the field and 39.8 percent from three. Irving might have the more dazzling offensive highlight reel, but Hayward is Boston's best two-way player. In his absence, Brown and Tatum will need to contribute on a more consistent basis. Al Horford and Marcus Smart must also step up. The Celtics relied on their depth the past several seasons. They sacrificed some of that to acquire two star players this summer. Now, one of them is out with a long-term injury, and depth is suddenly a concern.

The Celtics will be fine in the long-term, especially if Hayward is able to recover from this injury and return to full health, but for this season, his absence means Boston is closer to the middle-of-the-pack in the East now than a front-running contender ready to dethrone LeBron and the Cavs from their perch atop the East. The 2017-18 season was supposed to be a long journey for this group of Celtics players to figure out just exactly how far they could go. Instead, less than six minutes into a season brimming with optimism, everything has changed.