Knicks center Isaiah Hartenstein, left, blocks a shot by Celtics...

Knicks center Isaiah Hartenstein, left, blocks a shot by Celtics forward Jayson Tatum (0) during the second half of an NBA game on Dec. 8 in Boston. Credit: AP/Charles Krupa

GREENBURGH — While the Knicks’ concerns might be focused on healing three missing starters and trying to get all of their pieces in place, the measuring stick, however ill-timed, will arrive at Madison Square Garden on Saturday night when the Boston Celtics come to town.

They don’t have all of their pieces intact, but the Knicks still find themselves tasked with proving they can play with Boston, which already has beaten them three times this season.

The Celtics have all of their players, including superstars Jayson Tatum and Jaylen Brown. Their other starters, Kristaps Porzingis, Jrue Holiday and Derrick White, all made a case for an All-Star berth.

And still, the Knicks insist that there is no backing down from the challenge of the prime-time, nationally televised game in front of them.

“Yeah, that’s like the mentality you have to have to be successful in the league,” Josh Hart said. “Obviously, they have a team that has two All-Stars, Jrue has been an All-Star, Derrick was on the cusp, KP has been an All-Star. We know that.

“But at the end of the day, I’m going to take our roster and our team over anybody in the league. That’s the mentality you have to have. I think once we get back healthy and full swing, then everyone gets accustomed to playing with each other, I think we can beat any team. But that’s just the mentality we have. We have guys that can score, guys that can rebound, that can defend, that do the dirty work, guys that can hustle. We got a roster — we fill a lot of holes.”

Hart has inherited a starting job in the absence of Julius Randle, OG Anunoby and Mitchell Robinson, and at times seems to play every position. He certainly embodies the toughness the Knicks believe can lift them to the level of the star-filled teams.

The Knicks (34-22) were ascending toward the Celtics in the Eastern Conference standings before injuries depleted their roster and they lost four straight before the All-Star break. But they returned to action with some of the pieces back and got back on track Thursday with a win in Philadelphia. They are 2 1⁄2 games behind the second-place Cavaliers and 1 1⁄2 games behind the third-place Bucks.

The Celtics are 44-12 — the best record in the NBA — and have won seven straight games. The Knicks know they will have to get through the Celtics to be considered a serious threat come the playoffs.

“Definitely. The way they’re playing, I mean, they’re the gold standard right now the way they’re playing,” Jalen Brunson said. “So we’ve got to be up for the challenge, lock in, be ready to go. They present a great challenge for us. A lot of respect for them over there. We’ll just see where we’re at.

“I think it’s an indicator of where we’re at, no matter what the playoffs hold, because we’re not even thinking about that right now. We have 26 games left. And so right now we’re just obviously, we’re not at full strength. But we’ve got to find a way to be better every single day no matter who’s out there. Just our mentality.”

Notes & quotes: Coach Tom Thibodeau said all three players who returned from injury on Thursday — Donte DiVincenzo, Bojan Bogdanovic and Isaiah Hartenstein — came through the game fine. While the first two had starring roles, Hartenstein played only 11 minutes. “Just the game,” Thibodeau said. “That’s why I was saying to you guys, the minutes thing is more of a guideline and you have to read how the game goes, too. It’ll come for him.”

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