Ben Stokes' father, Ged, has been admitted to hospital in Johannesburg after suffering from what the ECB has termed "a serious illness".
Ged, who has travelled to South Africa with other members of the Stokes family to watch Ben in action, was taken ill on Monday night. He remains in a critical condition. Ben was expected to spend Tuesday at his father's bedside and did not attend training. A decision on his participation in the Boxing Day Test will be made in due course.
England's captain, Joe Root, said he was not sure if Stokes would be available, but had words of support for the allrounder.
"All I want to do is stress the importance of respecting the privacy of Ben and his family," Root said. "All the players and the squad want to throw our support behind him. It's crucial that comes first. We've got extra people out here and we feel like we've got a good squad to put out a competitive team."
Ged, a former New Zealand rugby league player, is in his early 60s and lives in Christchurch. He is a regular and popular figure at matches involving Ben and, on the face of things, appeared to be in robust good health.
Chris Woakes, meanwhile, has become the latest England player to come down with sickness, and did not train on Tuesday. England's preparations have been disrupted by a bug that prevented Stuart Broad, Jofra Archer and Jack Leach from taking part in the warm-ups.