Newcastle will face a Birmingham team that will also be much changed from their regular Championship line-up.
But a pathway to the last 16 is up for grabs if Newcastle can be successful on home soil and then see off Michael Appleton’s Oxford at the end of the month.
Benitez hinted at the type of team he’ll put out and said: “We know Oxford are waiting. At the same time, though, I want to put players out there that can guarantee we can do well on the pitch.
“We have to protect the team, so I can’t risk any player that has a knock or a problem. We know that Rotherham is also very close.
“We’ll try, I always say the same, we can go through using our squad. If we can’t then we can’t, but we have to try with the players who are ready and fit to play.”
Benitez is likely to turn to Ireland striker Daryl Murphy with the ex-Ipswich Town man looking for his third goal in as many games.
“He is a really good professional and a player who can score goals in this division,” he said.
“That’s been very helpful in recent games. Hopefully he can be an important player for us for the rest of the season.
“It also means we have balance in terms of experience and young players, that is always important because it gives you a boost in difficult circumstances.”
United could also field Cheick Tiote with the Ivory Coast international still on the books at St James’ having been unable to secure a January move.
Benitez said: “We’re still waiting for something concrete. He’s still training well.
“We’re still happy with him and he can play if we need him.”
Newcastle will also include Yasin Ben El-Mhanni and Dan Barlaser in their squad tonight due to injuries for Dwight Gayle, Isaac Hayden and Vurnon Anita.