Several members of England's touring party are ill with flu-like symptoms, a week before the start of the Boxing Day first Test in South Africa.
The conditions of Stuart Broad, Jofra Archer and Jack Leach, all absent from this week's warm-up match, have worsened, while "two to three" other players have also fallen ill.
England said that two members of their backroom staff have similar symptoms.
They added that they hope to see improvements within the next 72 hours.
As a consequence of the sickness in the camp, Friday's warm-up against South Africa A has been downgraded from its first-class status.
England will play four Tests, three one-day internationals and three Twenty20 matches during this tour, before moving on to Sri Lanka in March.
The tourists began with a draw against a Invitation XI in Benoni.