It was announced this week that Jacob Artist will play the younger relative of Mark Salling's alter ego when season four of the Fox series debuts in the fall.
Asked how the new arrival will impact Glee, Brennan told The Hollywood Reporter: "He's vastly different from any character we've had on the show in a really interesting and surprising way.
"There's great reveals with that character. We might have a star on our hands."
Artist, meanwhile, admitted that he has been kept in the dark about major aspects of his Glee character - including whether he will sport Puck's signature mohawk.
"[He has] a little bit of an attitude, so we'll see if that gets in the way of him succeeding with the glee club," Artist said.
"It'll be interesting to see how he reacts with everybody else as well to the new kind of Puckerman... All I know is that he's a bad boy. But it'll be fun to see where they decide to go with him."
A new love interest for Rachel (Lea Michele), played by Terra Nova's Dean Geyer, will also be introduced in future Glee episodes.
The show returns to Fox on September 13. In the UK, the show airs on Sky1.