The No. 1 team in the nation has a major March Madness scare on its hands.

Duke freshman phenom Cooper Flagg, the projected No. 1 pick in the 2025 NBA Draft, sprained his left ankle and was placed in a wheelchair during the ACC Tournament on Thursday.

Flagg did not return to the top-seeded Blue Devils’ 78-70 quarterfinal win against the eighth-seeded Yellow Jackets, but X-rays were negative, head coach Jon Scheyer said.

The big man is a “real long shot,” though, for Friday’s semifinal vs. arch rival North Carolina, per the coach.

“He was swollen already,” Scheyer said. “It’s not about being ready to go (Friday). That’s not the most-important thing for us. We got to see if we can get him right this run that we can make in the tournament, but I would have to be really convinced that we should even consider seeing if he can go (Friday).

“He may not be able to go anyway. He probably won’t be able to go anyway, but I think it’s a real long shot.”

The severity of this injury could have massive implications on the upcoming NCAA Tournament since the Blue Devils are a projected No. 1 seed and have the second-best odds at DraftKings to cut down the nets.

Flagg, who entered the game averaging 19.4 points and 7.6 rebounds, is their premier player.

The 6-foot-9 star suffered his injury Thursday when he landed awkwardly while going for a defensive rebound with less than three minutes remaining in the half.

Flagg grabbed the rebound with the Blue Devils trailing, 26-17, but then dropped the ball after his left ankle turned at a nasty angle.

He had to be helped to his feet and put his arms around his teammates before walking to the bench.

Flagg eventually left the court for the locker room, and was later captured being wheeled in the bowels of Spectrum Center in Charlotte.

Duke trailed Georgia Tech, 31-26, entering the half, but rallied to take the lead and advance to the semifinals.

Flagg emerged from the locker room early in the half to cheer on his teammates from the sideline.

He tallied two points on 1 of 7 shooting, including 0-for-3 from deep, while notching four rebounds in 15 minutes.

The Blue Devils also lost junior forward Maliq Brown due to a left shoulder injury.

It seems Duke will now be without Flagg when they try to beat their in-state rivals for the third time this season, and he may not be used either Saturday in the final, should the Blue Devils down the Tar Heels.

North Carolina could really a use win to bolster a rather uninspiring tournament resume.

The greater question is whether Flagg will be ready for the NCAA Tournament.

The Blue Devils are projected to be the No. 1 seed in the East Regional and could be the top overall seed, and would begin their championship quest either next Thursday or Friday.