England have suffered a blow ahead of Saturday's first Test against South Africa in Bloemfontein.
Harlequins wing David Strettle will miss the game because of illness, and has been admitted to hospital in Johannesburg for rehydration and monitoring.
Strettle is a victim of the stomach virus that has affected a handful of England players, and he will be replaced in the starting line-up by Gloucester's Iain Balshaw, who moves up off the bench.
A replacement for Balshaw among the substitutes will be announced on Friday after England train in Bloemfontein.
Team doctor Simon Kemp said: "David's vomiting continued through yesterday (Wednesday) and he was unable to take fluids by mouth. He was therefore admitted to a local hospital for rehydration and monitoring.
"And while he has made good progress overnight, he will not be fit to play on Saturday."
Centre Andy Farrell, meanwhile, was advised to take further rest on Thursday and did not train, but England say he is making good progress from his virus.
England head coach Brian Ashton said: "I obviously feel for David as it is his first tour, but Iain is an experienced player and will do a good job for us."
England's preparations for the Autumn International series were potentially dealt a further blow as Maro Itoje was forced to undergo an x-ray after Saracens' European victory over Scarlets on Saturday night.