David Bendingham fulfilled the role in the recent Test series against Australia, with scores of 49, 46, 0, 50 and 11 not enough to keep his place in the squad.
De Zorzi was injured for the Australia series and comes straight back into contention, with 17 Test matches already under his belt and averaging just more than 30 that includes two centuries and three fifties.
Hamza, meanwhile, has played just eight Tests - the last coming in February 2024 - with only one fifty to his name but has been prolific in domestic first-class cricket with an overall average of more than 48.
"The last thing I want to do is create what would look like a bit of a revolving door with that number three position. It definitely isn't that," Conrad said.
"Against Australia, I felt that, especially at the top of the order, we required a certain character, especially against the short ball plan, which I'm expecting to continue throughout the summer with Bangladesh up on the Highveld, as well as England on the Highveld.
"With Zubi and Tony coming in, we've still got a couple of days, so I'm not going to pick one yet. Tony is coming back from injury and Zubi is in really good form this year for both the Lions and the A side and is a natural number three.
"We'll see how the next couple of days pan out but one of the two of them will bat at number three and the other one won't play."
Conrad also confirmed that fast bowler Anrich Nortje will most likely miss the Test against Bangladesh as he makes his way back from a groin injury.
With Gerald Coetzee not in selected in the squad, one of Corbin Bosch or Dane Paterson could fill the third seamer role in support of Kagiso Rabada and Marco Jansen.
With the pitch at the Wanderers set to be quick and assisting the fast bowlers, Bosch could get the nod due to his extra pace while Paterson is slower but brings control.
When asked what he is expecting conditions wise, Conrad added: "It's stock standard. It's obviously hot here. We just hope that it's not over-prepared and ready too early.
"It's got a really good grass covering. I'd like to think we'll get a Wanderers wicket of old where there's good pace and balance because I think our attack can bowl on good wickets.
"We can take 20 wickets on good wickets. And we certainly want to give our batters every chance of posting big totals."
Zubayr Hamza and Dane Paterson have been recalled to the Proteas starting line-up as the hosts made two changes for the first Test against Bangladesh, starting at the Wanderers on Sunday.
Marco Jansen has been named ICC Player of the Month for October after playing a crucial role in the Proteas' Test series victory against Australia.
Australia seamer Mitchell Starc has returned to the top of the ICC Test bowling rankings after reclaiming his spot from Proteas all-rounder Marco Jansen.
David Bedingham has been dropped from the Proteas squad for the two-match home Test series against Bangladesh, with Tony de Zorzi and Zubayr Hamza recalled to bolster the batting unit.
