WALTHAM — Avery Bradley  came into this season as a question mark. He leaves it as a potential future cornerstone.
Bradley had surgery on Friday for his injured shoulder, which had repeatedly popped out during the playoffs. It’s a huge loss for the Celtics , who have come to rely on his tenacious on-the-ball defense and the jolts of athleticism he provided the offense.
“Avery’s a big blow. There’s no doubt. If I’m the guy on the other team and I don’t have to play against Avery Bradley, I would sleep a little better,” Doc Rivers  said. “No one wants to play against Avery. Our guys don’t want to play against him in practice. He’s a pain in the ass defensively. That’s what he does, and that’s not here anymore.
“We’re a great defensive team. What Avery did was allow us to be a great defensive team and put an individual on one guy and say, ‘Go shut him down.’ We don’t have that anymore. So now we have to go back to being just a great defensive team.”
Bradley’s loss has an effect on everyone on the court, but his absence is most acutely felt by Rajon Rondo . With Bradley in the game, Rondo didn’t have the responsibility of guarding the ball. That hasn’t meant as much for Rondo against the 76ers, who have several guards who can attack off the dribble, but at the same time, losing their best perimeter defender puts the Celtics at a disadvantage.
“It’s so unfortunate,” Ray Allen  said. “This season has probably been one of my more challenging seasons just from a team perspective just because we lost so many guys. Probably one of the more resilient teams that I’ve had because we’ve had so many guys step up and play well. My heart goes out to him because I know what he’s dealing with, I’ve been dealing with it myself.”
Beyond the ramifications for this season, Bradley’s emergence has been an unexpected revelation. As a rookie, he could barely stay on the court. In his second season, he not only established himself as one of the best on-the-ball defensive guards in the league, he also found ways to contribute offensively.
Bradley developed a knack for cutting to the basket and showed the strength and athleticism to finish inside. He also mastered the art of the corner 3-pointer, knocking down 56 percent of his attempts. With Bradley as a starter, the Celtics offense suddenly became dynamic and efficient, scoring over 112 points per 100 possessions.
“His growth this year has been terrific,” Rivers said. “He’s become a very valuable piece of this basketball team.”
It remains to be seen if the Celtics can go forward with an undersized backcourt and have it hold up over the course of an 82-game season, but one way or another, Bradley is a vital part of their future, and that’s not something anyone could say with certainty even three months ago.