The next scan on Wayne Rooney's broken foot will now take place on 7 June - a week earlier than originally planned.
Rooney, 20, had been due to fly to Germany with the rest of the England World Cup squad on 5 June, returning a week-and-a-half later for the scan.
However, it was decided at a meeting on Monday to bring that date forward.
The deadline for England to change their squad is 9 June, which means now they will have time to replace Rooney should the scan provide bad news.
If the scan had remained on 14 June, and if Rooney had been passed unfit for the tournament, England would not have had the option of replacing him.
England manager Sven-Goran Eriksson said: "It is important the scan will be done before I have to give the list to Fifa on 9 June. After then I can't change it.
"We have to take the decision and we want to have the scan as close to that date as possible.
"I have always been very optimistic and still think he will play a part in the World Cup"
"To have had the scan on 14 June wouldn't mean anything. The request came from us but it is up to Manchester United (Rooney's club) and when they heard our reasons they were very helpful.
"We are happy United accepted the scan on the 7 June."
Jermain Defoe of Tottenham and Andy Johnson, set to move from Crystal Palace to Everton, are the strikers standing by to replace Rooney if he cannot play at the World Cup.
If the scan shows that the fourth metatarsal in Rooney's right foot has healed, he would have three days to get fit for England's first group game or, more likely, two-and-a-half weeks to prepare for the first knockout round match should England qualify.
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But Eriksson added: "I have always been very optimistic and still think he will play a part in the World Cup."
The England coach insisted, however, that he is eager to play down the Rooney situation because it is completely overshadowing the team's World Cup preparations.
"Rooney is a very special football player, one of the best in the world, but we sometimes forget we have another 22 players in the squad," Eriksson said.
"There is too much talk, writing about Rooney's foot. It was the same in 2002 about (David) Beckham's foot.
"So, until 7 June I will not talk more about Rooney's foot. It is a pity he is injured but I feel a bit guilty. We have 22 other players in the squad and the only talk is of Rooney. It is enough now."
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Meanwhile, Rio Ferdinand insisted England will cope if Rooney is ruled out of the competition.
"The whole nation, including the players, are sitting with fingers crossed," Ferdinand said.
"We don't take it into consideration. If he's not fit it'll be a great blow but there are players who can come in."
Monday's meeting, at Manchester United's Carrington training ground, was attended by Sir Alex Ferguson, Eriksson and medical experts from Rooney's club and the national team.
A statement issued by Manchester United read: "It has been agreed to obtain a further precautionary CT scan on June 7 in order to help the England management to make a decision (on Rooney's fitness) before the deadline of 9 June.
"Both parties agree that everything possible is being done to aid recovery of a fracture that involves the joint."
The last line of that statement represents the first confirmation that Rooney's fracture involves a joint.
A report on the Manchester United website said the fact that a joint was involved meant it was "an injury which takes longer to heal".
That news - and the fact that the scan has been brought forward to before the deadline to calling up a replacement - means the development is being seen as negative news for the England striker.