Bentancur has sat out Spurs' last seven domestic matches due to a Football Association suspension for racist remarks about captain Son Heung-min earlier this year.
The absence of the 27-year-old Uruguay international has occurred at the worst time for head coach Postecoglou, who has been without a string of senior players for a jam-packed December and watched his depleted squad struggle for consistency.
"Even the injured guys, they are around the group all the time and they want to help, they want to contribute," Postecoglou said.
"They know we're in a tough moment and, for Rodrigo, it has been even more frustrating because it's not an injury which has kept him out.
"As I've said, he made a mistake, served his punishment now and wants to help the team.
"It's good to have him back. He's been working hard at training. In terms of Boxing Day, we'll see, but certainly (a boost) just to have an extra body.
"I think what the players have had to deal with, the core group of players over the last sort of three weeks or so, has been very, very demanding on them.
"Most of them have got through it pretty well, in terms of not getting any more injuries, thankfully for us, but it'll be nice to have just some ability to rotate some players and even make substitutions in games that hopefully will help us."
Spurs' joint-leading scorer this season is Brennan Johnson with 10 goals, but he has been restricted to a place on the bench in the last three matches with the in-form Dejan Kulusevski preferred at right forward.
Postecoglou insisted there is "nothing more" the Wales international needs to do to force his way into the team ahead of a return to old club Forest.
However, two logical solutions for Postecoglou to freshen up his starting line-up at the City Ground would be to recall Bentancur and Johnson - potentially in place of Yves Bissouma and Pape Sarr.
Asked what more Johnson needed to do, Postecoglou replied: "Nothing more. He has to just keep doing what he is doing.
"Obviously we have the balance of the team and we've had Deki there and Deki has done really well, scored in the last five games.
"It is just the balance of the team. Part of it is again, we don't have a lot of options up there and it is about managing that load.
"We're already overburdening a couple of players in that area, so it is good to have Brennan, who we are managing through this period and he'll play significant minutes."
Tottenham are in need a positive result in Nottingham, but will come up against old boss Nuno Espirito Santo, who has turned Forest from relegation candidates into Champions League hopefuls during his 12 months in charge.
"He obviously came here and it didn't work out for him, which just happens, but he's shown he's a top manager and he's doing a fantastic job at Forest," Postecoglou said.
"They've got some quality players in there and they're having a really good season. Particularly at their place, it's going to be a great challenge for us."
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