Wasps lock Simon Shaw will fly to Australia, after X-rays confirmed that Danny Grewcock has broken his hand.
Bath captain Grewcock suffered a blow to his left hand during England's victory over Uruguay in Brisbane on Sunday.
"Danny has broken his hand. He is having further X-rays today, but it is 99.9% he will be ruled out," said England head coach Clive Woodward.
"Simon Shaw is on the way now, but you cannot make a replacement until it has been cleared by Rugby World Cup.
"So as we sit here now, Grewcock has not been ruled out medically. Once that is done, Shaw will join the party."
Grewcock's latest injury is his second since England arrived in Australia.
He suffered a broken toe when a team-mate accidentally trod on his foot during the pre-match warm-up before the Pool C opener against Georgia in Perth last month.
The Uruguay game was Grewcock's first appearance in the tournament after recovering from that setback.
The 30-year-old Shaw missed out behind Grewcock, Martin Johnson, Ben Kay and Martin Corry in Woodward's original squad.
At the time, Woodward described his omission as one of the toughest selection calls he has had to make during his six years in charge of England.