This had been shaping up to be the year the Boston Celtics were finally unbothered by injury. But Avery Bradley’s shoulder popped out of its socket once too many times, he might undergo surgery any day now, and the Celtics suddenly rest one loss away from a possible end to the Big Three era, or one win away from Ray Allen and his damning bone spurs defending Dwyane Wade for 30-plus minutes per contest.

When the season started, who would have figured a Bradley injury would prove so much more critical than the one Allen suffered in March?  Allen’s bone spurs allowed Bradley to find himself and the Celtics to stumble inadvertently upon their best lineup. Bradley’s injury now forces a struggling Allen back into the starting lineup, and shines a brighter spotlight on the struggling duo of Mickael Pietrus and Keyon Dooling. With Bradley, Rajon Rondo could freely roam off the opponent’s non-ball-handler, using his gambling for good. Without Bradley, Rondo’s gambling turns into paint touches for Jrue Holiday, Allen spends more time being abused by younger, more athletic, healthier players, and Boston’s bigs spend far too much of their time attempting to cover for the guards’ mistakes, all of which led to Philadelphia’s 42-16 advantage in points in the paint last night.

Avery Bradley has not shot well during the postseason, not at all, but the Celtics are 20 points per 100 possessions better in the postseason when he is on the floor. That’s good enough for the second-best on-court/off-court number on the Celtics, and third isn’t even close. His defense hides many of his teammates’ inadequacies. His athleticism helped transform the Celtics, and especially comes in handy against the league’s elite physical specimens, guys like Holiday or Wade.

The Celtics still will, and should be, favored against the 76ers in Saturday’s Game 7. They are at home, and they are experienced, and they still have the three best players in the series, though Philadelphia might now have 4-12. But last night, watching Philadelphia’s guards break down the Celtics defense, watching how the Sixers shot 46 percent even while shanking several wide open jump shots, watching how old and slow and even disinterested the Celtics appeared, it hit me like a Jeep driving 95 MPH — Boston is as vulnerable right now as an open wound.

“Bradley is a pit bull on the ball,” Lou Williams said last night, according to the Boston Herald. “Obviously his (absence) is hurting them a little bit and some other guys had to come in and we were able to exploit the mismatches.”

With no key offensive contributions from the bench and Allen misfiring on all cylinders, the Celtics need monster performances from Rondo, Paul Pierce and Kevin Garnett — or, at the very least, all three of their stars need to arrive at the gym on time and ready to play. Rondo, who shot 4-of-14, mustered just six assists and acted as an automatic door for Sixers penetration, was not present last night at the Wells Fargo Center. He will likely improve in Game 7. After all, he can’t be very much worse.

The Celtics can of course win without Bradley. They did so in Game 5, convincingly. But without him, their small margin of error reaches  microscopic levels. Their team defense needs to be connected on a string. They need to run offense with a purpose. They can succeed without him, but without him, this is the very same lineup that started the season 15-17. Many things have of course changed since then. Garnett spent the second half of the season making a belated campaign for the All-Star game. Rondo isn’t normally (with last night being the exception) quite so inconsistent. Pierce played himself into shape. The Celtics, even without Bradley, are better than the team that began the season 15-17.

But this was supposed to be the season without an asterisk, the year the injury gods finally repaid the Celtics by striking deadly blows to all their opponents while leaving the Cs untouched. Bradley could still come back, as if by a miracle. But it’s unlikely.

I hate it, and I hope the Celtics can overcome this one more piece of adversity during a season that’s been filled with mountains of it. But I can already see the asterisk being drawn.

*Before Avery Bradley’s injury, this team looked like a real challenger.

So rise up, Celtics. Prove me wrong. Wipe that goddamn asterisk away. Once more, show us never to declare you dead before your vital signs disappear.