Steyn suffered a heel injury on Saturday at Newlands where South Africa are hosting India in the first Test.
"During Dale's 18th over, he landed awkwardly in the footholds, causing significant strain in the foot, leading to tissue damage on the underside of the foot in the heel area", South Africa team manager Dr Mohammad Moosajee, who is also a medical doctor, said according to Cricbuzz. "We'll add him to the squad and then when we get to Pretoria and have a couple of training days we will have a look and make a decision", he added.
Steyn appeared to have made a successful return, taking 2-51 in India's first innings to improve his career total to 419 wickets in 86 tests.
Significantly, South Africa has strengthened its hold on India in the first Test match. "He is unable to do much at the moment so he will be reassessed in 4 - 6 weeks".
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Steyn will see an ankle specialist on Sunday, Moosajee said, after which a timeline on his recovery would be clearer.
A team spokesman said the injury was being assessed and treated.
Steyn, 34, had not played in a first-class match since suffering a fractured shoulder in a Test in Australia in November 2016. Before that, the paceman, regarded as one of the game's great fast bowlers, endured other problems with his right shoulder and a groin injury. Now he will not play in this match.