Duminy ruled out of the series
CSA said in a statement the left-handed batsman and part-time spinner would undergo surgery to re-attach the tendon on Saturday morning and could be out of action for up to six months.
Duminy, 28, who was expected to support a four-pronged pace attack with his off-spin, hurt his left ankle in a fall during a team training run after South Africa had reached 255 for two. He had to be helped off before being taken to hospital for a scan.
“At first assessment JP said he heard a loud clicking sound and it felt like he had been hit by an object,” South Africa team manager Dr Mohammed Moosajee said.
“The diagnosis of an Achilles' tendon rupture was confirmed by the MRI scan in the evening and he will undergo surgery to re-attach the tendon on Saturday morning.
“We will only be able to gauge further down the line on an expected recovery date, but injuries of this nature have been known to take up to at least six months before the player can resume playing cricket.”
Twelfth man Francois du Plessis will field in place of Duminy, who played a major role in South Africa's first Test series win in Australia four years ago.