Senior internationals Chris Robshaw and Danny Care have been left out of England's first World Cup training squad.
The Harlequins pair, with 150 caps between them, are not part of a 29-man group named by the Rugby Football Union.
But four uncapped players are in the squad - Bath wing Ruaridh McConnochie, Gloucester's Georgia-born prop Val Rapava Ruskin, Northampton flanker Lewis Ludlam and Harlequins back-row forward Alex Dombrandt.
Bristol-bound number eight Nathan Hughes also misses out, and whether another absentee - Northampton hooker Dylan Hartley - is called into camp at any point this summer remains to be seen.
Hartley, who led England to Six Nations titles in 2016 and 2017, has not played for six months due to a knee problem and it is understood that he is still struggling with the issue.
Saracens fly-half Owen Farrell is an overwhelming favourite to captain England at the World Cup in Japan.
Apart from Rapava Ruskin and Ludlam, players from clubs involved in the Gallagher Premiership semi-finals - Saracens, Exeter, Gloucester and Northampton - will not feature at this stage due to a mandatory five-week rest period.
The pair, plus a small number involved for an England XV against the Barbarians on June 2, will be managed to ensure post-season active rest periods are fulfilled in agreement with Premiership Rugby and the Rugby Players' Association.
Flanker Robshaw, 33, was England's 2015 World Cup captain, but he last featured for his country a year ago, and 32-year-old scrum-half Care did not gain selection during last season's Six Nations.
The squad will assemble at Pennyhill Park in Surrey on Sunday for five days, before a second camp from June 30-July 4 when further Gloucester and Northampton players could be added.
England boss Eddie Jones is due to name an official training squad on July 4, boosted by a potentially sizeable Saracens and Exeter contingent, before the first official World Cup camp begins three days later.
Jones said: "The first two England training camps are designed to improve individual players' fundamentals to allow them to compete for a place in the Rugby World Cup squad."
Ruskin, 26, was born in Tbilisi, but moved to England at the age of two. He is a former Georgia Under-19 captain who played for Worcester before joining Gloucester.
Former England Sevens star McConnochie enjoyed an outstanding debut season with Bath last term and Dombrandt, who was a colleague of Wales flanker Aaron Wainwright at college in Cardiff, and Ludlam have also maintained impressive club form.
Saracens forwards Mako Vunipola and George Kruis, meanwhile, will attend the training camp for treatment.
Harlequins' Mike Brown is in the group despite not playing for England for over a year and he is determined to make an impact.
"Getting selected in this squad is the first of many steps to getting selected for the World Cup," said Brown on Quins' official site.
"There's a long way to go but I am going to give everything I can to get picked."
England's World Cup warm-up fixtures begin with a match against Wales at Twickenham on August 11.
England squad for first World Cup training camp
Forwards: D Cole (Leicester), T Curry (Sale Sharks), A Dombrandt (Harlequins), T Dunn (Bath), C Ewels (Bath), E Genge (Leicester), J Launchbury (Wasps), L Ludlam (Northampton), V Rapava Ruskin (Gloucester), N Schonert (Worcester), B Shields (Wasps), K Sinckler (Harlequins), J Singleton (Worcester), S Underhill (Bath), M Wilson (Newcastle)
Backs: C Ashton (Sale Sharks), M Brown (Harlequins), J Cokanasiga (Bath), E Daly (Wasps), G Ford (Leicester), J Joseph (Bath), J May (Leicester), R McConnochie (Bath), D Robson (Wasps), M Smith (Harlequins), B Te'o (Worcester), M Tuilagi (Leicester), A Watson (Bath), B Youngs (Leicester)