The Somerset left arm spinner, who has struggled to fully recover from sepsis he picked up during the tour of New Zealand in November and was also struck with gastroenteritis and flu ahead of the first Test at Centurion last month, has not been able to reach the expected levels of fitness to be considered for selection.
The England medical team, in consultation with Leach, felt to recover fully it would be beneficial for him to return to the United Kingdom. He will leave South Africa on Thursday.
“It has been an unfortunate time for Jack with illness and since the Test series in New Zealand six weeks ago, he hasn’t been able to get 100 per cent fit,” said England head coach Chris Silverwood.
“This has hampered his preparation in South Africa and despite his best endeavours he is not in a position to make himself available for selection for the final two Test matches.
“He is a great lad to have around the squad and his infectious personality and popularity will be missed. However, his focus has to be getting himself better and receiving the optimum levels of recovery and treatment, which is best served back in England without any distractions.
“I have no doubt that he will return to full fitness in the medium-term and hopefully he will recover in time for our tour of Sri Lanka in March.”