The actor joined the show this season as Sebastian, a "villain" who could come between Blaine (Darren Criss) and Kurt (Chris Colfer).
He has appeared in two episodes so far, 'The First Time' and 'Hold On To Sixteen'.
Gustin will now recur for the rest of the current season and will be a series regular in the fourth, E! Online claims.
However, a spokesperson for Fox did not confirm the news and Gustin wrote on his Twitter page that he does not know whether he will be returning as a regular.
"Thanks for all the congrats but this news is not official as of yet," he told his followers. "I would love to be sticking around. I'll be waiting for official word."
Glee returns with a new episode on January 17 at 8/7c on Fox.
> Glee Grant Gustin talks Sebastian, Kurt & Blaine and dream songs