South Africa have cancelled Saturday's planned intra-squad practice match after a second member of their squad tested positive for Covid-19.
They are due to begin their limited-overs series against England in Cape Town on Friday 27 November.
The unnamed player has been moved to separate accommodation and is isolating away from the team.
On Wednesday three South Africa players were put in isolation following the previous positive Covid test.
"Team management and Cricket South Africa (CSA) are in close communication with their counterparts from the England Cricket Board to ensure full transparency and the most responsible plan of action going forward," said CSA in a statement on Friday.
England will play three Twenty20s and three one-day internationals, all behind closed doors.
The tourists were tested before departure and again when they arrived at their team base in Cape Town on Wednesday.
- Watch Premier League football live on BBC iPlayer: Fulham v Everton - find out more here