Fast bowler James Anderson is set to return to the England side for the second test starting in Cape Town on Saturday, boosting their chances of a repeat win as South Africa declared their front-line bowler Dale Steyn doubtful.
England's record wicket taker continued his recovery from a calf strain by bowling six overs in the nets on Wednesday, as England clinched the first at Kingsmead by 241 runs, to add to a practice session on Tuesday.
"He is hopeful of playing and it's looking good but we'll know in the next 48 hours," said captain Alastair Cook.
But Steyn, who broke down on Monday with a shoulder injury, is far from certain to be fit for South Africa, who struggled without his pace and aggression in the first test.
"Dale might not be fit in time but we'll make that decision on Friday but I certainly hope he does play," said South Africa captain Hashim Amla.
"Our options are limited without him, he's our banker bowler."
Steyn, ranked number one in the world, had scans on his shoulder after pulling up in the early stages of England's second innings and eventually bowled just 22 balls.
The scans did not reveal any muscle damage and South Africa suggested it was a shoulder spasm, but Steyn was unable to bowl again.