CLEVELAND — The gruesomeness was followed by heartbreak. The Celtics carried big dreams and aspirations into this season, and 5 minutes, 15 seconds into it Tuesday night, Gordon Hayward suffered one of the most ghastly injuries in recent memory.

His left ankle turned at a 90-degree ankle, Hayward was sitting on the court under the basket at Quicken Loans Arena helpless, writhing in pain, pointing to his leg while Cavaliers players on the bench in front of him covered their faces with towels.

Hayward is likely out for the season. The maximum-salary free agent and small forward the Celtics had coveted for years will soon begin a long recovery process. Meanwhile, there are 81 games left to play after a 102-99 loss to LeBron James and the Cleveland Cavaliers and the Celtics have to devise a contingency plan just to compete.

Their chances of overcoming the Cavaliers and winning the Eastern Conference diminished considerably after Hayward’s injury. He was supposed to relieve the scoring load from Kyrie Irving and Al Horford.

So what now? How does the brilliant Brad Stevens compensate for the absence of an All-Star? There are no easy answers.

Elite players aren’t replaceable, so the Celtics are going to have to make an attempt by committee. The injury immediately places more pressure on Jaylen Brown to develop, and the 20-year-old responded after the injury with a team-high 25 points.

First-round draft pick Jayson Tatum also is going to have to play beyond his 19 years, which is unfair, but life in the NBA isn’t fair. Tatum looked lost on the court at times Tuesday, getting snuffed by James in a “come stronger than that, kid’’ sequence in the first quarter. He missed his first five shots but finished the night with 14 points and 10 rebounds.

Tatum will get better and more confident but it seems unreasonable to depend on him right away. Speaking of green, Semi Ojeleye, the second-round pick, played nine scoreless first-half minutes. The Celtics have depth, but it’s young depth and suddenly the maturity curve no longer exists.

Marcus Smart missed his first nine shots, and finished a dismal 5-for-16 from the field. But that didn’t stop his aggressiveness, and as the game progressed, Smart became more confident and used his svelte body to attack the basket and post up a defenseless Kyle Korver. Smart definitely is playing with a personal agenda. On Monday the Celtics passed on the opportunity to sign Smart to a contract extension, making him a restricted free agent next summer.

He likely will slide into the shooting guard position depending on the matchup. His 3-point shot — hitless in four attempts Tuesday — still needs major work, but Smart brings a toughness and physicality the Celtics relish and Hayward’s unfortunate absence will provide him more of an opportunity.

One key component in moving forward is swingman Marcus Morris, who will miss the first week or so of the season because of knee soreness. Morris was expected to start when he was acquired for Avery Bradley, but his progress has been slowed by an assault trial (in which he was found not guilty), lack of basketball shape, and the sore knee. Morris can add a dimension of scoring, toughness, and rebounding when he returns to form in a couple of weeks.

What’s frustrating for the Celtics is Hayward was just getting comfortable in the offense. In addition to a scorer, he’s a playmaker and facilitator. The Celtics aren’t going to replace that. They are going to have to push forward with crisp ball movement, and even more offensive production from Irving and Horford.

If Hayward is ruled out for the season, the Celtics could apply for a disabled-player exception and pursue a player through trade with the additional salary cap space. There are free agents who may be able to help; Gerald Green was just waived by the Milwaukee Bucks.

But expect president of basketball operations Danny Ainge to take his time in making the right decision for both the short- and long-term future. The Celtics already were deep at the swingman position, and it could be just a matter of letting Brown and Tatum grow, improve, and flourish as they did in the second half against the Cavaliers.

This was a devastating night for the Celtics, a crushing injury to a standout player. Gordon Hayward was going to contribute greatly to the Celtics’ quest of overcoming Cleveland in the Eastern Conference. The organization has to be concerned about his long-term prognosis beyond this season.

There is a full season left to play, however. After looking shell-shocked in the first half, the Celtics came back strong in the second half, playing with passion and vigor.

Irving took over in the fourth quarter but came up short on a couple of late attempts.

Tatum played beyond his years after the jitters and Brown stepped up his game. The Celtics now return home Wednesday night against the Milwaukee Bucks with a major quandary on their hands. They will have to figure out how to move on, but the certainty is they will move on.

Gary Washburn can be reached at gwashburn@globe.com.