Jon Flanagan and John Stones both flew to Vale do Lobo with the 23 members of the squad on Monday morning, while Michael Carrick, Tom Cleverley, Andy Carroll and Jermain Defoe remain on standby - and all face an anxious wait to see if they will get their opportunity.
And Mills, who was handed his chance to represented England at the 2002 World Cup due to injuries, told TheFA.com he expects them to approach the trip with the mentality of a first-team player.
England's World Cup schedule
- Portugal training camp: 19-23 May
- Peru at Wembley: 30 May
- Miami training camp: 1-7 June
- World Cup begins: 12 June
“Someone always gets an opportunity to make a name for themselves and to perform on the biggest stage,” he said. “I was one of those – I got lucky. Gary Neville got injured and I had an opportunity.
“World Cups only come around once every four years and you don’t get that many opportunities – especially if you’re a fringe player – to play, so you have to make every second count, whatever your status in the group.”
Mills won 19 caps for England – including the five he earned in the 2002 World Cup where he played every minute of the Three Lions’ campaign, until they eventually lost out to Brazil at the quarter-final stage.
And the former Leeds United, Middlesbrough and Manchester City man said that those heading out to Portugal, Miami, and finally to Brazil will be giving everything they have to become a part of football history.
Danny Mills played every minute of England's 2002 World Cup campaign
“Training is always going to be intense,” he added.
“Even for those 12 that aren’t involved, they are right at it. That’s what makes the competition so fierce because to play in a World Cup it’s just unbelievable.
“Even in your wildest dreams as a kid you never believe it’s actually going to happen and suddenly when you get that opportunity you have to take that chance.”
England return from Portugal on Friday 23 May and take on Peru at Wembley on 30 May – in their final preparation game on home soil before the World Cup.
