London - England coach Stuart Lancaster has dropped five players from his initial 50-man pre-tournament Rugby World Cup squad, the Rugby Football Union announced Friday.
The remaining 45 players will now head off to a high-altitude training camp in Denver, Colorado as they battle to make the final 31-man squad which Lancaster, like all World Cup coaches, must name by August 31.
Veteran back-row forward Nick Easter has been omitted, although their is a possibility he could be recalled, as have rising stars Maro Itoje and Elliot Daly.
Meanwhile, lock Ed Slater and fly-half Stephen Myler have also been dropped.
Easter will remain with club side Harlequins for treatment on a back problem whilst the quartet of Itoje, Daly, Slater and Myler will now be on standby for tournament hosts England's squad.
"The players have worked very hard for the past three weeks and there is a really good feel about the group," said Lancaster.
"Denver is the next stage in our training, a chance to develop further in a different environment."
The uncapped duo of Wasps centre Daly and Saracens lock Itoje must wait for their international chance, although Lancaster said both had "bright futures".
"Elliot and Maro have fitted in and trained well and it's been great for them to be in this environment," the coach said.
"They are both young players who have bright futures. They have made a great impression and I am sure other opportunities will come for both of them further down the line.
"Steve and Ed, likewise, have contributed greatly. Ed has done well to recover from his knee injury having missed the majority of last season. However, there is a lot of competition in the second row.
"I have spoken to all the players to explain that things can change very quickly and they can come back in at any point."
Lancaster said injury was the reason why 36-year-old Easter, a member of the England side beaten by South Africa in the 2007 World Cup final, was not travelling to the United States.
"Nick will stay for treatment on his back rather than risk aggravating it further with travel," he said.
"We look forward to him rejoining the squad in August when we will review the squad and also consider those who have been unable to begin the camp after suffering injuries at the end of last season."
England's 45-man squad will spend two weeks in Rugby Town USA in Glendale, Colorado.
England 45-man World Cup squad
Fullbacks: Mike Brown (Harlequins), Alex Goode (Saracens)
Wings: Chris Ashton (Saracens), Jonny May (Gloucester), Jack Nowell (Exeter), Semesa Rokoduguni (Bath), Anthony Watson (Bath), Marland Yarde (Harlequins)
Centres: Brad Barritt (Saracens), Luther Burrell (Northampton), Sam Burgess (Bath), Kyle Eastmond (Bath), Jonathan Joseph (Bath), Billy Twelvetrees (Gloucester)
Flyhalves: Danny Cipriani (Sale), Owen Farrell (Saracens), George Ford (Bath), Henry Slade (Exeter)
Scrumhalves: Danny Care (Harlequins), Lee Dickson (Northampton), Richard Wigglesworth (Saracens), Ben Youngs (Leicester)
Backrows: Calum Clark (Northampton), James Haskell (Wasps), Matt Kvesic (Gloucester), Ben Morgan (Gloucester), Chris Robshaw (Harlequins), Billy Vunipola (Saracens), Tom Wood (Northampton)
Secondrows: Dave Attwood (Bath), Courtney Lawes (Northampton), Joe Launchbury (Wasps), George Kruis (Saracens), Geoff Parling (Leicester)
Props: Kieran Brookes (Newcastle), Dan Cole (Leicester), Alex Corbisiero (Northampton), Joe Marler (Harlequins), Matt Mullan (Wasps), Mako Vunipola (Saracens), David Wilson (Bath)
Hookers: Luke Cowan-Dickie (Exeter), Rob Webber (Bath), Tom Youngs (Leicester), Jamie George (Saracens)
World Cup warm-ups
August 15, Twickenham: England v France 21:00
August 22, Stade de France: France v England, 21:00
September 05, Twickenham: England v Ireland 16:30
World Cup pool matches
September 18, Twickenham: England v Fiji 21:00
September 26, Twickenham: England v Wales 21:00
October 3, Twickenham: England v Australia 21:00
October 10, Manchester City Stadium: England v Uruguay 21:00