Hooker Dylan Hartley has been left out of England's World Cup training squad after failing to recover from a knee injury.
Hartley, who captained England to back-to-back Six Nations titles in 2016 and 2017, has not played since December and the omission has increased the chances of him missing the tournament in Japan.
Experienced scrum-half Danny Care and flanker Chris Robshaw also missed out on the 29-man training squad announced by head coach Eddie Jones on Thursday.
Care, who has 84 England caps, did not feature in this year's Six Nations, while Robshaw has not played for his country since having knee surgery in October.
Forwards Alex Dombrandt, Lewis Ludlam and Val Rapava Ruskin and back Ruaridh McConnochie have received their first international call-up.
McConnochie, who plays for Premiership side Bath, represented Team GB in rugby sevens at the 2016 Rio Olympics.
In a statement, Jones said that the training camp allow previously uncapped players to compete for a place in the Rugby World Cup squad.
Jones can only pick players who were not involved in last month's English Premiership semifinals for his first training squad, due to regulations which state that all players involved must be put on mandatory rest for five weeks.
That means Saracens' fly-half Owen Farrell and lock Maro Itoje, as well as Exeter Chiefs' centre Henry Slade and winger Jack Nowell -- who underwent ankle surgery on Wednesday -- are unavailable. However, injured Saracens pair Mako Vunipola and George Kruis have been called in for medical treatment.
Players from losing semifinalists Gloucester and Northampton Saints will join the camp next week and Jones will name his final training party, including players from Premiership finalists Exeter Chiefs and Saracens, on July 4.
The first training camp will be held at Pennyhill Park, Surrey (June 23-27) followed by another at the Lensbury, London (June 30-July 4).
The Rugby World Cup kicks off on Sept. 20 with England facing Tonga in their opening Pool C encounter in Sapporo two days later.
England training squad
Dan Cole (Leicester Tigers), Tom Curry (Sale Sharks), Alex Dombrandt (Harlequins), Tom Dunn (Bath Rugby), Charlie Ewels (Bath Rugby), Ellis Genge (Leicester Tigers), Joe Launchbury (Wasps), Lewis Ludlam (Northampton Saints), Val Rapava Ruskin (Gloucester Rugby), Nick Schonert (Worcester Warriors), Brad Shields (Wasps), Kyle Sinckler (Harlequins), Jack Singleton (Worcester Warriors), Sam Underhill (Bath Rugby), Mark Wilson (Newcastle Falcons).
Chris Ashton (Sale Sharks), Mike Brown (Harlequins), Joe Cokanasiga (Bath Rugby), Elliot Daly (Wasps), George Ford (Leicester Tigers), Jonathan Joseph (Bath Rugby), Jonny May (Leicester Tigers), Ruaridh McConnochie (Bath Rugby), Dan Robson (Wasps), Marcus Smith (Harlequins), Ben Te'o (Worcester Warriors), Manu Tuilagi (Leicester Tigers), Anthony Watson (Bath Rugby), Ben Youngs (Leicester Tigers).
Information from Reuters contributed to this story.