The annual Barbarians clash comes just six days before England Saxons' Churchill Cup campaign continues a final group of fixtures ahead of England manager Johnson announcing an enlarged World Cup training squad.
His cut-off date to then name the 30 players who will travel to New Zealand is August 22, which follows World Cup warm-up games against Wales (home and away) earlier that month, and comes five days before facing Ireland in Dublin.
Saxons head coach Stuart Lancaster - a rumoured contender for the Rugby Football Union's new performance director post that Sir Clive Woodward last week ruled himself out of the running for - will take charge of preparations to tackle the Barbarians.
And players in the spotlight look set to include a Gloucester quartet of Paul Doran-Jones, Dave Attwood, Luke Narraway and James Simpson-Daniel, Northampton's in-form number nine Lee Dickson and his potential half-back partner Charlie Hodgson.
A 24-man squad though, also includes 13 uncapped players, with the likes of Exeter flanker Tom Johnson and Harlequins prop Joe Marler among those hoping for a chance.
Lancaster said: "It is a great opportunity for all the players who are looking to force their way into Martin Johnson's plans for the World Cup, and those who will go on to defend the Churchill Cup with the England Saxons next month.
"We face a very big challenge against the Barbarians, who have a very experienced squad in terms of their average age and number of caps.
"But there is a great deal of quality in the England system at the moment, and a lot of these young players will get a chance to benchmark themselves against the best.
"We've seen that in the way the likes of Ben Youngs, Courtney Lawes, Alex Corbisiero have taken their chances recently.
"A lot of the players have played in big games recently, both in Europe and the Premiership.
"If we combine them with some of the more experienced players like Paul and Charlie Hodgson, Ugo Monye and James Simpson-Daniel, it should be an exciting combination."
No players from Leicester or Saracens were available for the non-cap Barbarians game because of Saturday's Premiership final between the clubs at Twickenham, but several are probable Churchill Cup squad selections.
The Barbarians squad, which includes the likes of Sergio Parisse, Martyn Williams, Doug Howlett and Paul Sackey, is due to be finalised tomorrow morning.
And there is expected to be a place in the 25-man group for Australian rugby league international Willie Mason, who yesterday switched codes when he joined wealthy French club Toulon.
Mason has courted controversy throughout a chequered and colourful career in the 13-man code, and made only six appearances for Hull Kingston Rovers this year before being de-registered after failing to obtain a Tongan passport which would have made him a non-overseas player.
Rovers then stopped paying his wages after discovering he had gone behind their backs to talk to Toulon owner Mourad Boudjellal, before releasing him from his three-year contract.
Although he has never played rugby union, Mason revealed yesterday that he is set to play for the Barbarians against England and then against Wales in Cardiff six days later.
"I am just so excited to be playing rugby and I'm looking forward to the challenge," Mason told the Sydney Morning Herald.
"I've certainly jumped in the deep end in agreeing to play for the Barbarians without having any rugby experience.
"If you ask all the boys, I've always told them I've wanted to have a crack at rugby (union), and I'm ready to try the best I can to make an instant switch."
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