As much as they will surely miss Horford, they knew Big Al well enough to know that the decision was one made with careful thought and consideration.
But that doesn't change the fact that him latching on with the Philadelphia 76ers was a double-whammy in weakening their roster while significantly bolstering the title hopes of a rival.
And so on the eve of the first meeting against Philly with Horford in tow on Wednesday, it only magnifies the loss of Horford being anything but an average blow.
But in losing Horford, Boston finds itself with little choice but to go with a bigs-by-committee approach heading into Wednesday's season opener at Philly.
And of the bigs in that mix, none can defend or stretch the floor beyond the 3-point line the way Horford did for years in Boston.
Marcus Smart is the longest-tenured Celtic, having seen lots of teammates come and go through the years.
But Horford's decision to opt-out of the final year of his deal in Boston and re-sign with Philadelphia admittedly caught him off guard.
"In a way, yeah, but not really," Smart said when asked if he was surprised Horford signed with the Sixers. "He stayed in the East. They're a championship-contending team. They're really good. Al wants to win. He gave his time here and he felt it was time for a new chapter in his life."
Jaylen Brown, who recently agreed to a four-year deal worth as much as $115 million, said he has not spoken to Horford since he signed with Philly but quickly added, "But I always wish him the best. That's my guy."
Brown quipped, "He's probably sitting back somewhere, icing his knees. That's my guy."
While many Celtics fans were stunned when Horford opted out of his contract with Boston and signed elsewhere, Horford's decision to leave did not come as a surprise to Brown.
"Not a lot surprises me; the NBA is crazy," Brown said. "It wasn't that I was expecting him to leave, but I wasn't surprised that he did. Everybody has to do what's best for them. Al's been in this league a long time; he's a vet. He earned every paycheck he's gotten. I wasn't surprised he went and took care of his family."
The Celtics will see first-hand Horford's impact on both ends of the floor - not so much in what he does but what his presence opens up for the Sixers and their All-Star center Joel Embiid.
Meanwhile, the Celtics will counter with a variety of big men that Boston will be counting on to help soften the blow of losing Horford.
But no one within the Celtics organization is disillusioned to believe that the loss of Horford will be easily filled by one of the players that comprises Boston's bigs-by-committee group.
"Al was a great guy; he taught us young guys a lot when he was here," Boston's Daniel Theis, in the running to start at center for Boston on Wednesday, told NBC Sports Boston. "None of us are going to go out there and be Al. That's not who we are. We just have to do things a little differently now that he's not here; that's all."
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Replacing Al Horford not the average challenge for the Celtics originally appeared on NBC Sports Boston