Ferguson said: "Gabby's agreed he's going to sign permanently, we've just got to iron out a few things.
"It's a big signing for the club and shows where we want to go."
Zakuani has been a virtual ever-present in defence for Ferguson's side since his arrival in September.
The deal cannot be completed until the transfer window opens on 1 January owing to Football League loan rules.
As a result, Zakuani will miss matches against Leicester, Millwall and Cheltenham in the second half of December.
Nevertheless Ferguson is confident Zakuani will prove to be an excellent capture for the club.
"He's an out and out defender, but he also knows he can improve," Ferguson said.