He plundered 17 off the Indian right-armer in the 9th over of the innings.
The fast bowler's initial reaction at the time of the injury suggested that it was nothing serious - although he stopped his run-up and immediately threw the ball to Vernon Philander to complete the over, he jogged part of the way off the field, stopping occasionally to grab his boot. According to espncricinfo, he may not bowl again in this Test.
The type of injury normally takes 4-6 weeks to heal, Moosajee added, nearly certainly ruling Steyn out of the rest of the series against India and putting a question mark over whether he can once again regain full fitness ahead of Australia's tour in March.
Steyn will see a specialist on Sunday, Moosajee said.
Dale Steyn pulled up midway through his 18th over, on Day 2, with a bruised left heel.More news: Tamil Nadu Transport Minister appeals to bus employees
Steyn managed to make 16 before South Africa were bowled out for 286 when Morkel was trapped lbw off the bowling of Ravichandran Ashwin for two runs. "Just feeling very sympathetic for him".
Steyn, 34, had not played in a first-class match since suffering a fractured shoulder in a Test in Australia in November 2016.
"That one over from AB changed the game", said Benkenstein.
His comeback was closely watched with fears that he hadn't played enough cricket in the buildup to this season and might struggle for match fitness. It is important to note that this unfortunate injury was freakish because of the way he landed in the footholes.
Further joy was to come for the raucous Cape Town crowd as Morne Morkel removed captain and dangerman Kohli (5) with his first ball, India closing on 28-3 and leaving Cheteshwar Pujara and Rohit Sharma with the sizeable task of rescuing their reply. Azharuddin, who was captain when India played their first Test in South Africa way back in 1992-93, felt the current team stands out when it comes to pace bowling and feels Kohli's men are well prepared despite not playing a warm-up game.