England midfielder Steven Gerrard said it would be "impossible" for England to succeed in this summer's World Cup without striker Wayne Rooney.
Rooney was injured in Saturday's game at Chelsea
The 20-year-old's participation is in doubt after he broke a bone in his foot playing on Saturday against Chelsea.
"It would be a disaster for England if we had to go to the World Cup without Wayne. He is idolised around the country and is our main man," he said.
"I think it is impossible to have a successful World Cup without Wayne."
Gerrard was ruled out of England's World Cup campaign in 2002 because he needed a groin operation.
He said the experience of watching the team's progress on TV was a "nightmare".
"I know Wayne will be desperate to go, so fingers crossed he can recover quickly from this," said Gerrard.
"Hopefully he won't have to go through what I went through in 2002. From experience I can tell him that it is a nightmare back home watching a World Cup on the TV."
Former England boss Sir Bobby Robson said England's World Cup chances would be seriously affected if Rooney were to miss all or part of the campaign.
"It's depressingly sad. Without him we would go from possible World Cup winners to outsiders," Robson told BBC Radio Five Live.
"We can't replace him. I don't think there's another player like him in the country - or even in Europe."
Robson said Rooney had the quality to influence this summer's tournament in Germany.
"People who win World Cups are top individuals. Who won the World Cup for Argentina in 1986? I'll tell you - it was Diego Maradona," he said.
Robson, who is now a consultant for the Republic of Ireland national team, said Rooney must be taken to Germany - even if there was only a chance of him playing later in the tournament.
England's opening Group B match is on 10 June - exactly six weeks to the day after Rooney's injury.
But should they progress, their first knock-out game would not be until 24 or 25 June, with a quarter-final taking place on 30 June or 1 July - potentially giving Rooney three extra weeks to recover.
"What you need is your top players for the quarters, semis and final. That's when Rooney becomes crucial," said Robson, who took England to the World Cup semi-final in 1990.
"If you can get him back for the quarter-finals then you take a chance and take him."
Chelsea and England midfielder Joe Cole, who some have tipped as a possible replacement for Rooney, said the striker could defy the medical experts.
"Knowing Wayne, he will be back quicker than predicted by the medical team because that's the sort of character he is," he said.
Cole said the injury caused concern for everyone at Stamford Bridge, including Chelsea fans who were already celebrating their side's title as they led 3-0 when Ferreira tackled Rooney.
The midfielder said: "The game was gone and everyone in the stadium just thought: 'Oh no, the World Cup, is Wayne going to be all right?'.
"He's a mate and you don't want to see anyone get injured, especially at this time with the World Cup around the corner. That would probably have been the first thing that crossed his mind."
He added: "Whatever they tell him he'll be out for, I'm sure it will be half that or three-quarters of that because he's got that winning character."
Former England and Tottenham star Gary Mabbutt said he did not expect Rooney to be ready for the World Cup group matches.
But he said it did not spell the end of England's World Cup hopes.
"I'm sure now that he's not going to be available, probably, for the first few games," Mabbutt told BBC Radio Five Live.
"The players there are going to want to show exactly what they can do - and I think their games are going to be raised by the fact that Wayne's not there to start with.
"Now, Wayne didn't score in any of the qualifying games. Overall, I don't think it's a total disaster."
Chris Waddle, who won 62 caps for England playing on the wing, said he was certain Rooney would still go to the World Cup, even if he was not fully fit for the start of the tournament.
"He's definitely worth taking if they think he'll be fit for the quarters," he told BBC Radio Five Live.
"He's not obviously going to train as well, or as hard, as he'd like to. He will be behind, we've seen that with David Beckham in 2002 when he had a similar injury."
Waddle said Liverpool's Steven Gerrard could play a key role up front for England should Rooney be unavailable.
"I've looked at permutations and you could play Shaun Wright-Phillips on the right and move David Beckham inside with Frank Lampard," he said.
"You could play Steven Gerrard in Rooney's role. He's got the talent and he's played there for Liverpool many times."
Former England skipper and BBC pundit Terry Butcher said the time it took Rooney to recover from his previous fractured metatarsal did not bode well.
"When Rooney broke his metatarsal in Euro 2004, it took a long time for him to come back and reach the level of performance he likes to play at - and that Manchester United and England need," he told BBC Radio Five Live.
"Also, from a Manchester United point of view, I wouldn't be happy if I was Sir Alex Ferguson, sending out Wayne Rooney to the World Cup in a bid to try and get him fit for England.
"That could backfire and put him out into the new season for Manchester United, so there's lots of other things to think about."