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South Africa's plans for the third Test against England were thrown into turmoil when wicketkeeper Quinton de Kock slipped and hurt his knee, ruling him out of the match at the 11th hour.
The Proteas have called up Dane Vilas as cover but he has to fly in to Johannesburg from Port Elizabeth, where he was due to represent Cape Cobras.
Should South Africa field first, captain AB de Villiers will keep wicket until Vilas arrives at the Wanderers.
Proteas team manager, Dr Mohammed Moosajee said: "'Quinton slipped and sprained his right knee at home late yesterday afternoon. Initially he didn't think it was too serious but woke up after midnight in pain and with a swollen knee. He will have investigations done later today to ascertain the extent of the injury."
Vilas scored a career-best 216 not out for Cobras last week.