Centurion - England will have to make "a very late call" on their playing XI for the first Test against South Africa, starting at Centurion on Thursday, captain Joe Root said on Tuesday.
With all-rounder Ben Stokes at the bedside of his critically ill father and Chris Woakes the latest victim of illness that has swept through the touring squad, Root admitted that the build-up to the four-match World Test Championship series had been "frustrating".
But Root said he was confident that England could field "a very competitive team" even if some leading players were not available.
Stokes' father Ged was admitted to hospital in nearby Johannesburg on Monday with what an England statement said was a "serious illness".
Fellow all-rounder Woakes did not train on Tuesday because of illness, but Root said the recovering Stuart Broad, Jofra Archer and Jack Leach were making good progress. "We will have to keep them monitored over the next couple of days and see how things go."
Root did not speculate on the chances of Stokes being able to play.
"It puts things in perspective," he said.
"We need to play good hard cricket and win this series but most important for us as a squad is we need to make sure that Ben and his family get all the support they need."
The England captain added: "It's been quite frustrating in many ways but we have to handle it and get on with it and make sure the guys who are selected are ready to go.