Grant Hill says he’s already been crushed by Knicks 6-foot-9 rookie forward Kevin Knox.

“Duke wanted him badly — he was first on the radar, I heard from coaches,’’ Hill told The Post.

“We were all heartbroken. He’s a really good kid, got a great skill set. But it has been a little up and down.”

Hill, a former Duke star, will call the Knicks-Celtics game from Boston at 8 p.m. Thursday as the Knicks make their season’s first appearance on TNT.

Knox chose Kentucky, but Hill said he believes if Mike Krzyzewski wanted him that badly, he’s worth the pick and is not a softie. Knox, the Knicks’ 2018 lottery selection, is shooting a horrific 33.8 percent. After his 27-point breakout game Saturday in the Milwaukee OT thriller, Knox had a letdown in Monday’s loss versus the Wizards (eight points, 3-of-11).

Hill lives in Orlando and followed Knox’s high school career in nearby Tampa.

“He went out in Las Vegas [in summer league] and did very well and now he struggles a little bit,’’ Hill said. “I’m not too down on that. All rookies, they figure it out at their own pace. I do think he has tremendous upside and is trying to figure it out. He’s learning about the game — pace, talent level. I think his skill set, size, character, basketball intellect — I do think he has a chance to be a really good player in the league.’’

Hill, part of the new ownership group of the Hawks, saw the Knicks in Atlanta last month on one of Frank Ntilikina’s finest offensive nights. Nevertheless, Ntilikina, the Knicks’ 2017 lottery pick, is on the outs — not having played the past two games after going scoreless in the previous two contests.

“In person I was blown away with his size,’’ Hill said. “Good length, good athlete. I still think he’s raw and needs to get his shot and ball-handling tighter. He has good things to work with. That’s a tough position.”

Teams are looking for more from their point guard nowadays than just being a quarterback, Hill said.

“In this day and age, you don’t have to be a facilitator/decision-maker, but you have to be able to put the ball in the basket and shoot,’’ Hill said. “There’s loads of examples of point guards who weren’t great shooters and worked at it and became good shooters.

“If he can develop his shot, I love his length and potential on the defensive end. Like a few of the guys they have, they’re trying to figure out who they are. It may take some time. Not everybody is going to come in like [Kristaps] Porzingis and have an impact right away.”

As the youngest team in the league, Hill sees the Knicks (8-17) at the same stage as Orlando a few years back. Hill said the Magic gave up too soon on some of their youngsters — Victor Oladipo, Tobias Harris, Elfrid Payton, though held onto the emerging Aaron Gordon.

“[Coach David Fizdale] is giving them an opportunity to develop young players,’’ Hill said. “They don’t get better unless they play. It may not result in wins but establishing a foundation for success. By and large, they’re competing.”

Like his Hawks, the Knicks are likely competing for lottery position, too. His fellow Dukies, Zion Williamson, RJ Barrett and Cam Reddish have given also-rans greater motivation to be in the lottery, Hill acknowledged.

“They are really talented, potential stars in the NBA,’’ said Hill, who does some Hawks scouting and is in the war room. “Some of the bottom feeders, there’s an excitement with the possibility of some of these Duke players.’’

Diplomatically, Hill said “flip a coin’’ on which of the three will be the best pro. But he seemed most dialed in on Williamson, the beastly 6-foot-7, 280-pound forward whom he believes can be revolutionary.

“Athleticism, basketball feel, IQ, that size and athleticism is quite remarkable,’’ Hill said. “And it’s how hard he plays. Plays hard every possession. He has the tools to revolutionize the game with his play but he’s still young and learning. His upside is something special. It’s exciting. Talking with coaches at Duke, he’s one of the hardest workers. He’s a grinder and competes. Combined with his God-given ability, his mindset gives him a chance to be really special in the NBA.’’

In the last meeting, the Knicks upset the Celtics in Boston on Thanksgiving Eve — a low point to their disappointing 13-10 start. Hill predicts potential changes in a month or so. The Celtics are grappling with having essentially two starting point guards in Kyrie Irving and Terry Rozier, each of whom would look good in orange and blue.

“They’re still figuring it out,’’ Hill said. “Another month will be very telling. If they don’t turn it, there could be some changes, personnel moves. With that payroll and talent level, you get into late January and are still struggling as they are, conventional wisdom has moves being made.’’