It is almost a month since Borini was initially thought to be on his way back to the Stadium of Light in a deal reported to be worth £12million after impressing in a loan spell last season.
Liverpool's inability to recruit another striker is said to be holding up the deal, but Poyet is determined to land the former Chelsea man ahead of the new Premier League season.
"It's still ongoing," Poyet told American satellite radio station SiriusXM.
"It's important. Fabio, for us, is important and I will tell you why.
"You can always go and spend some millions on a player, but when you know the player the way I know Fabio, how professional he is, how much he cares, the positions in which he can play, and what he brings to the team and to the group.
"He has plenty of things that I really, really like. He's professional and I think he would be fantastic for the group as well, not just because he scores goals.
"He's a key player, which is why the (fee) agreement with Liverpool is quite a big one.
"We’ll see. I'm still hoping it is going to happen, but we need to wait and see."
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