Back-row Mercer, who has been ineligible for England selection since departing Bath for Montpellier in 2021, is included in the preparation camp as he is joining Gloucester ahead of next season.

With no players involved from Premiership semi-finalists Saracens, Sale, Leicester or Northampton, due to the requirement for player rest, 36-year-old Harlequins scrum-half Care is a surprise recall.

Gloucester loosehead prop Rapava-Ruskin, who is Georgian-born and an U19 international for Los Lelos, also makes the squad, and is currently uncapped at senior level.

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Meanwhile, Billy Vunipola (Saracens), Ollie Chessum (Leicester Tigers) and Luke Cowan-Dickie (Exeter Chiefs) will attend the camp to continue their respective rehab programmes.

"We are excited to get into camp and begin the first phase of our preparations," said Borthwick.

"The World Cup is full of top-quality teams and high-quality players, and we're relishing the challenge in front of us. That all starts today at Pennyhill Park.

"We have lots to get through before our first Summer Series fixture in August against Wales in Cardiff, so the hard work starts now. We are looking forward to it."

The England squad assembled at their Rugby Performance centre in Pennyhill Park on Monday, with their opening World Cup warm-up clash on Saturday August 5 against Wales in Cardiff.

Borthwick will announce his final 33-player Rugby World Cup squad on Monday August 7, with England's Rugby World Cup campaign beginning against Argentina in Marseille on Saturday September 9.

England's initial 28-player RWC training squad:

Forwards (15): Jamie Blamire (Newcastle Falcons), Alex Dombrandt (Harlequins), Tom Dunn (Bath Rugby), Charlie Ewels (Bath Rugby), Ellis Genge (Bristol Bears), Ted Hill (Bath Rugby), Joe Marler (Harlequins), Zach Mercer (Montpellier), Beno Obano (Bath Rugby), Tom Pearson (London Irish), Val Rapava-Ruskin (Gloucester Rugby), Kyle Sinckler (Bristol Bears), Will Stuart (Bath Rugby), Sam Underhill (Bath Rugby), Jack Walker (Harlequins)

Backs (13): Henry Arundell (London Irish), Danny Care (Harlequins), Joe Cokanasiga (Bath Rugby), Ollie Hassell-Collins (London Irish), Will Joseph (London Irish), Ollie Lawrence (Bath Rugby), Joe Marchant (Harlequins), Jonny May (Gloucester Rugby), Cadan Murley (Harlequins), Harry Randall (Bristol Bears), Henry Slade (Exeter Chiefs), Marcus Smith (Harlequins), Ben Spencer (Bath Rugby)

Greenwood: Mercer gives England great options at No 8 | 'England need to build as are miles off world's best'

Former England Rugby World Cup winner Will Greenwood told Sky Sports...

"Zach Mercer has been outstanding. Top 14 player of the year, and as he is returning to an English club in Gloucester, he can be included for this World Cup.

"I was lucky enough to work with the Barbarians in November and two of the best coaches in the world, Ronan O'Gara - who took La Rochelle to another European Cup trophy - and Scott 'Razor' Robertson - who is the Crusaders head coach, and incoming New Zealand one. Zach was part of that squad, and is a heck of a kid.

"He's done amazingly well. He wasn't getting picked for England three or four years ago, and I believe was supremely brave to move to France.

"Sometimes as players, you can think about moving abroad and taking a chance and experiencing another culture, but sometimes players cling on for what might be. He didn't wait, he just went, carved it up in France, played so well, and now gives England some really good options at No 8.

"Billy Vunipola returning from injury, Alex Dombrandt and now Mercer into the pot. So it's a position of real strength in that back-row.

"I don't think we're going to see playing from the back with this squad. It's very much get rid of it, get it down the far end of the field, live off mistakes, and if an opportunity arises, try and take it.

"Steve Borthwick will be trying to build on that. Because the reality is, England are miles away from where they should be in terms of the top four or five teams in the world.

"Steve's style with Leicester Tigers was a superb set-piece, and mitigating against weaknesses by simply removing them and not playing from areas of the field that could expose them."