England will make a late call on fast bowler Jofra Archer after he was unable to play a full part in training before the second Test against South Africa, which starts on Friday.
The 24-year-old is suffering with soreness in his right elbow.
"Not knowing exactly how Jofra is might change how we balance the side. He did pull up sore," said captain Joe Root
Paceman Mark Wood is yet to return to match fitness while spinner Jack Leach has been ruled out through illness.
Batsman Dom Sibley is expected to be fit after coming down with the sickness bug that has swept through the squad.
England lost the first of the tour's four Tests at Centurion in December.
The tourists will decide whether to persist with a bowling attack of five seamers or bring in the spin of Matthew Parkinson or Dominic Bess.