Avery Bradley had surgery on both shoulders, not just one as was originally reported. (WEEI)

As the Celtics prepare for Game 7 Saturday night at TD Garden against the Sixers, Avery Bradley is resting after surgery Friday on both shoulders, a source with direct knowledge of the situation tells WEEI.com.

The source confirms that Bradley had surgery on Friday and is expecting a summer-long rehab program that could last up to four months. If all goes as expected, Bradley should be ready for training camp in October.

Bradley initially injured the rotator cuff in his left shoulder but after playing with the injury, he also injured the right shoulder to the point where it needed to be repaired as well.

So as a 21-year old playing in his first NBA playoffs, with two shoulders in need of surgical reparation, Bradley managed to post the second-best postseason plus-minus numbers on the Celtics (behind Kevin Garnett).

I haven’t had enough time to reflect on Bradley’s unexpectedly ginormous contributions this season, but here’s a quick synopsis:

Bradley was so desperate to improve on his nothing rookie season that he spent a week at Doc Rivers’ Orlando house prior to the lockout. The lockout then robbed Bradley of a preseason for the second straight year, so, thirsty for on-court repetitions, he signed with a professional team in Israel.

He soon started the season as Boston’s first guard off the bench, but quickly lost his hold on that position to E’Twaun Moore after unleashing several outside shots that almost ripped holes through the backboard. When Rajon Rondo went down with an injury during the first few weeks of the season, Bradley was still the one called upon to fill in. He performed reasonably well and the Celtics went 6-2 during the eight games Rondo missed. That stretch included one game in Orlando during which Jameer Nelson (at least according to Bradley) audibly pleaded for Bradley not to apply such fierce pressure. Rondo’s absence provided the first extended period when we saw that Bradley could be relied upon in a bigger role, but still, we couldn’t foresee the leap he would take later in the season.

Sometime around the All-Star break, Bradley’s confidence grew like The Grinch’s heart did late in Dr. Seuss’ storybook masterpiece. The outside shots that previously threatened to decapitate onlookers suddenly swished through the nets. Doc Rivers told Bradley to be more like Andre Miller, meaning he should slash to the hoop whenever his defender turned his head, and Bradley became one of the league’s best backdoor cutters.  Being a great cutter doesn’t always equate to NBA stardom (see: Daniels, Marquis), but in Bradley’s case, his offense simply needed to be passable so his defense could burn bright like the sun.

People forget this, but it took more than Ray Allen’s injury for Bradley to be inserted into the starting lineup. In the first game Allen missed, Mickael Pietrus started in his place. But Pietrus went down with a concussion, Bradley became the starter by default, and Rivers had inadvertently stumbled upon his best lineup. The Celtics finished the season on a tear, and Bradley was a major part of their success. After hitting just four three-pointers over the first four months of the season, Bradley drilled 18 of 33 in the month of April. His offense obviously had stopped being an issue, and trying to score against him remained comparable to “getting stung by 507 bees simultaneously” on the list of things NBA players enjoy doing.

The playoffs arrived and Bradley stopped shooting so well, which might have had something to do with his two shoulders badly in need of surgery. But Bradley kept on trucking through the pain, even after needing someone to pop his shoulder back into its socket on numerous occasions. Through the injuries he remained a huge part of the team’s success, placing second on the Celtics in plus-minus numbers — behind only Garnett, whose positive impact on the Celtics has been borderline fiction.

Bradley’s season ended cruelly. His absence could prove crushing to the Celtics. But he’s 21, he’s already improved from “Mr. DNP” to “Mr. Indispensable,” and it’s easy to envision an NBA landscape where Bradley, alongside Rondo, is half of the league’s greatest guard tandem.

It ended too early, but Bradley’s season was a resounding success, and his future has few limits.