The Italy international, who joined the Black Cats from Juventus back in August, was not included in the matchday squad at the weekend.
Poyet is confident that the midfielder will play a crucial role as Sunderland seek to retain their Premier League status this season.
"People will ask why Giaccherini wasn't even on the bench; he's an Italian international and I know, it hurts," Poyet told the Northern Echo.
"I need him. Maybe he doesn't believe me, but I need him, because now if Fletch (Steven Fletcher) is not available then maybe we will need Giacchi there.
"And then he needs to help us, and I'm sure he will because he's a great professional."
Giaccherini has made 18 appearances for Sunderland.