Duke fans better enjoy Cooper Flagg while they can … ’cause Seth Curry tells TMZ Sports it won’t be long before the Blue Devils baller is starring on NBA courts.

Flagg’s currently got Duke rolling into the Sweet 16 of the NCAA tournament … but on Wednesday, Curry told us he has no doubts the freshman phenom will be lighting it up in the Association soon.

Steph‘s younger brother — who played at Duke from 2010-2013 — said Flagg can score and play defense with the best of them … and he didn’t push back when we said it certainly looks like the 18-year-old will be the No. 1 overall pick in this summer’s draft.

In Duke’s first two tourney games, Flagg’s been seriously impressive … scoring 32 total points while recording 16 rebounds and 11 assists. He’s expected to do more of the same later Thursday, when he and the rest of the Blue Devils face Arizona in Newark with a spot in the Elite Eight on the line.

Curry clearly believes Flagg and his alma mater are going to come away with a victory … telling us he’s “never felt better” about his old squad.

“They’re like an NBA team out there,” he said. “They’re huge, they’re moving around.”