Lancaster has been in talks with New Zealand's World Cup winning coach Wayne Smith about joining the England management team as backs coach through to the 2015 tournament.
Smith, who thrived in a similar management structure with the All Blacks, has already expressed his interest in the role and he is widely regarded as the best in the business.
But with Smith likely to be unavailable for England's summer tour to South Africa, Lancaster has turned his attention to finding a temporary third member of his senior management team.
Mike Catt, the London Irish backs coach, has been widely touted as the leading candidate for the temporary position alongside Lancaster and Graham Rowntree.
London Irish are not thought to have received an official approach from the Rugby Football Union for Catt, although that may not be necessary.
Catt has one year remaining on his London Irish contract but he is reportedly leaving the club this summer as part of a cull of backroom staff.
England are playing their first ever three Test series in South Africa and with two midweek games also in the schedule, Lancaster is taking at least 40 players and therefore a number of "support coaches".
But the structure of his core management team will remain the same as it was when he took over, initially on an interim basis, for the Six Nations.
"There will be three main coaches but to do this tour with just three coaches would be a stretch so we'll need some support in there too," Lancaster said in an interview to launch the new RFU.com homepage.
"Short term we need to find a replacement for Andy for the tour and some support coaches who can come in and help out with the team that plays in midweek.
"And also on the sheer logistics of it - we're going to select 40-plus players and we want to make sure we give them the feedback they deserve.
"Long term as well I want to make sure we've got the best coaching team to take us not only through the QBE Internationals this autumn and next year's Six Nations but right the way through Rugby World Cup 2015."
Lancaster argued strongly for the RFU to recruit Andy Farrell from Saracens on a permanent basis following the impact he made during his secondment with England during the Six Nations.
Two weeks after the RFU first approached Saracens, Farrell decided to remain with the Aviva Premiership champions.
Twickenham were accused in some quarters of dragging their feet.
"He had a massive impact on the players and on the environment and culture," Lancaster said of Farrell.
"He was brilliant for me and we had a fantastic journey through the Six Nations together.
"He had decisions to make after the tournament and I fully respect those decisions. We still have a great relationship and will talk all the time."
Lancaster flew to South Africa last Friday to meet with Smith, who is currently coaching Super Rugby side the Chiefs.
Smith has said he is committed to them until the end of their campaign but he would be interested in a role developing England's attacking game.
"Stuart Lancaster has done a hell of a job in his short time as national coach," Smith wrote in a recent blog on therugbysite.com
"If I was an England supporter I would be pretty excited.
"But Lancaster will know that as far as England have come, they will have to keep improving if they are to compete with the southern hemisphere.
"They play South Africa four times, New Zealand, Australia and Fiji before the end of the year.
"They won't beat those sides just smashing the ball up. They will need an attacking strategy by then and they will need alignment with all the coaches and players."
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