We have seen Marcus Smart go down too many times to count this season, only to rise after gathering himself.
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But what we saw in Boston's 113-104 win over the New York Knicks looked and felt different, more serious than the usual bumps and bruises he absorbs.
Smart drew an offensive foul against New York's Kevin Knox who delivered a hard-driving shoulder into Smart's abdomen, with him grimacing in pain similar to what we saw last spring when he suffered an oblique injury that sidelined for about a month.
It's too soon to say whether this latest injury is along those lines, but the idea of Smart missing some time is not a bad idea.
He is the heart and soul of this team.
That's not in question.
But he's also the King of the walking wounded club, a player whose body is covered with soreness, pain and all the bumps and bruises that come about form a player who throws his body around defensively with little to no regard for his general health.
And if we're talking about Smart missing significant time which is possible, the Celtics will be challenged moving forward in a way that we have not seen this season when other Celtics have gone down.
Not only does Smart play an integral role in the team's functioning at both ends of the floor, but the Celtics have no one on their roster even remotely close to providing what he does on a night-in, night-out basis.
When Boston has had one of their wings or bigs go down for a while with an injury, there was a clear direction which players would see an uptick in their minutes.
When Gordon Hayward suffered a hand injury last month, we knew that Jaylen Brown and Jayson Tatum would take on a more pivotal role, along with Brad Wanamaker off the bench.
And when any of the team's bigs-by-committee suffered an injury, it was easy to employ the "next-man-up" mantra and know that it would work.
But if Smart is out for any length of time, all bets are off on how well or woeful the Celtics defense will be, particularly when you consider how they have struggled so mightily in recent games.
Boston limited the Knicks to just eight made 3-pointers, but allowed New York to shoot better than 50 percent from the field most of the game.
The Celtics came into the game having allowed their previous three opponents to each make 17 or more 3-pointers, becoming only the seventh team in NBA history to do so.
And that was with Smart in the lineup.
Again, it's too soon to tell how long - if at all - Smart will be out for the Celtics.
But if he's anything less than 100 percent, the Celtics have to do their due diligence and save Smart from himself and sit him down for at least a game or two.
His body is as banged up as anyone you'll find in the NBA, with him playing through injuries to his fingers, a separate knuckle injury, a couple of ankle sprains and a sore hip.
And he has done so with no complaint, reminding me on Saturday that he has no plans to sit out any games if he doesn't have to.
"If I can go, I'm going," he told NBC Sports Boston. "But if I can't, I'll sit. I just feel as long as I'm able to do what I'm capable of doing, I can help this team. And if I feel or the medical staff feels I'm not healthy enough to do that, I won't play."
It appears that time might be upon us with Smart's injury on Sunday looking a lot more serious than his previous bumps and bruises experienced this season.
Don't miss NBC Sports Boston's coverage of Celtics-Heat, which tips off Wednesday at 7 p.m. with Celtics Pregame Live, and then Tommy & Mike have the call at 7:30 p.m. You can also stream the game on the MyTeams App.