Proteas captain Graeme Smith said he did not think there would be too much question about who would bowl if Steyn is fit.
"The three guys who've had the job over the last period of time have been very successful," Smith said.
"Makhaya (Ntini) brings a lot of experience to our attack. He maybe didn't bowl as well as he would have liked in Centurion (in the first Test), but he's a guy that I certainly support, and he's been integral throughout my captaincy, so I really back him to come through in this Test match and to bowl well.
"Morne (Morkel) offers you some variety in the attack with his pace and bounce, and it was great to see Friedel perform well (on debut in Centurion), but if Dale is fit, I think it will be a straight swap."
De Wet took three wickets in the space of six overs on Sunday afternoon to take South Africa very close to a thrilling victory in the first Test, which ended in a draw.
Smith said Steyn had been making good progress and had done some bowling in Cape Town, and he hoped a decision could be made on his availability by the night before the Test started.
The skipper added that all-rounder Jacques Kallis, who is recovering from a fractured rib, was also making good progress, but it was not yet clear how much he would bowl in the second Test.
"I would be a little conservative," Smith said. "Obviously to have him bowl at some stage would be great - it allows us some variety and some more options with the attack.
He said he would not be surprised if England named the same XI for the second Test.
"England seem to be sticking to the six batsman route," he said.
"I think, for them, it's a slightly more conservative outlook. They probably feel, after their middle order were troubled in both innings (in Centurion), that they need to have the extra batting available.
"But if we could get some early wickets up front, we'd like to expose that middle order."
Smith also said he was not too concerned about the England bowling attack.
"They've got some quality bowlers around, who've performed well over time," he said, "but in the Test matches we played in England last year, we played very well against their attack.
"We managed to post some very good totals at Headingley, we batted out two to three days at Lords, and in the fourth innings we chased a very good total at Edgbaston.
"So we've had some success against their attack and we batted well on a wicket that did a lot with the new ball in Centurion. The batting unit - especially the top six - has performed well against England over the past two years, and we'd like to carry that on."
Smith said the second Test in Durban offered new challenges for both teams.
"We would like to be the team that adapts best and be stronger than England in the first three days.
"At this time of year, the humidity is always a massive issue, and the overhead conditions. There has been a lot of rain around Durban, so how you look after the ball here is obviously crucial."
The skipper said he was not concerned that England would be targeting him with the new ball.
"Since I've taken over at 22 years of age, I've had to get used to that," he said.
"As a player, handling the captaincy and being a top-order batsman, going into a big series and being targeted, it's something I've dealt with and have been able to thrive on during my career. So I'm excited to have the opportunity to do that in this series."
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