England head coach Ashton admits it is not an ideal situation, but although he would not name the five World Cup probables, most educated guesses would point to Jonny Wilkinson, Jason Robinson, skipper Phil Vickery, Martin Corry and Tom Rees.
A severely-depleted England squad will head home from South Africa tomorrow, having conceded 113 points and 15 tries in suffering two crushing defeats against their main World Cup pool rivals.
By the time they meet again in Paris on September 14, England will undoubtedly have a vastly different look about them.
Many of those players involved during the past fortnight will miss out when Ashton names a likely 40-strong World Cup training squad on Wednesday week, with absent tourists from Leicester, Wasps and Bath returning in their droves.
England then meet up on June 25 ready for a 12-day camp in Portugal prior to August World Cup warm-up appointments with Wales and France (twice).
Ashton said: "Probably about five of the (World Cup) starting XV are definite, which is not how it should be at this stage of 2007. I am fully aware of that.
"In other positions in the team, it is a question of deciding which of two players is going to make the starting XV. It's not as though we have five players and then 10 complete blanks, we've got five and then 20 other players.
"In terms of the warm-up games, I think it is quite important we get the combinations we want on the field against America (England's opening World Cup opponents on September 8) to play together as often as possible before then."
Ashton reaffirmed that Leicester scrum-half Harry Ellis, Wasps prop Tim Payne and Gloucester back-row forward James Forrester will miss the World Cup through injury, but Sale Sharks fly-half Charlie Hodgson is expected to be in contention.
Hodgson has been sidelined since suffering a serious knee injury during England's autumn Tests more than six months ago.
Ashton added: "What I might do is announce a squad to train in Portugal, plus two others who are still in consideration for the final World Cup squad of 30, depending on what happens during the rest of the summer.
"Tim Payne has been eliminated, as have James Forrester and Harry Ellis, but Charlie Hodgson should be up and running by the time we go to Portugal. I am not sure about Mike Tindall (broken leg) - it depends on how he is healing."
Ashton accepts England have been widely written off as genuine World Cup contenders.
Even with a full-strength squad in Bloemfontein and Pretoria, they would have struggled to match a South African side that has emerged as New Zealand's biggest threat for global dominance.
As things turned out, a persistent stomach virus and injuries made an improbable task impossible, with South Africa displaying an imposing power game built around forwards like Schalk Burger, Pierre Spies, Victor Matfield and skipper John Smit.
There were plus points for England though, notably the perfomances of hooker Mark Regan, flanker Nick Easter and prop Kevin Yates, who all emerged as serious World Cup candidates, while Mathew Tait must be close to nailing down the outside centre spot.
Ashton said: "One of the things is that we have got to be able to match South Africa physically.
"Certainly, we can't afford to go on the field playing South Africa in the World Cup with half a team that physically is going to be outmatched, and conditioning work is an integral part of our preparation.
"It has been a difficult trip, but it was one we had to fulfil. Clearly, it was always going to be an enormous challenge, and to expect to beat the Springboks twice was probably unrealistic.
"I think you find out more about the character of the players in situations like this one.
"Three players went on the field in the first Test match not feeling well, and how the hell they managed to run around for 10 minutes, let alone 65 or 70, I don't know. They showed terrific character to do that.
"We would have wanted all the players training all the time and all the players available for selection for both games, but that hasn't been the case.
"A lot of the players will have known when they set foot on the plane their chances of making the World Cup training squad were less than some of those players who stayed at home, but they gave everything they got.
"We've learnt a lot about South Africa, but they probably haven't learnt a great deal about us."