The injury that ruled Quinton de Kock out of the third Test with England occurred when the South Africa wicketkeeper slipped while walking his dogs, team-mate Dean Elgar has revealed.
De Kock was a late withdrawal from the Proteas' line-up on Thursday, with Dane Vilas being summoned as an emergency replacement and only arriving at the Wanderers after play had begun.
South Africa merely cited a "freak injury" to De Kock as the reason for their last-gasp change, but opening batsman Elgar provided more detail after stumps had been drawn on the opening day in Johannesburg.
"Quinny said he was walking his dogs yesterday and he slipped and he somehow twisted his knee," said Elgar.
Vilas went on to contribute 26 on his return to the team as South Africa, who won the toss, ended the opening day on 267-7, with each of their top nine making double figures but no batsman passing 50.
"[We lost] maybe one or two wickets too many, but I think it's that kind of wicket where you can always lose one or two in quick succession," Elgar added.
"All in all, I think it was a good day for us. We've got to look for something that's a little bit above 300 - I think that would put us in a really good position.
"The wicket might quicken up a little bit and play into our favour."
Elgar was his side's top scorer with 46 and shared 73 with Hashim Amla (40) after initially seeing off the new ball alongside Stiaan van Zyl (21).
"They [England's bowlers] definitely threw a lot at us, especially the top three today," said Elgar. "They didn't give us a lot of scoring opportunities and they seemed to put the ball in the right area quite a lot.
"It was good to grind it out with Stiaan, and Hash as well, and I thought we got ourselves into a very good position with the first two partnerships."