Lancaster's position, and that of his coaching team, will not be decided until after their final pool game against Uruguay this weekend but the soul-searching from Saturday's costly defeat by Australia, a week after their capitulation against Wales, has begun in earnest.
Amid the stinging media criticism and apologies from players and management, England's defence coach Andy Farrell found himself in the firing line after suggestions, said to have come from forward Billy Vunipola, that he had too much influence on team selection.
The heavily bearded Farrell rebuffed such talk in backing Lancaster and urged the RFU to keep him in charge.
"The four of us as coaches get together and have discussions and ultimately Stuart makes the call and we all buy into that," he told reporters.
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"We've lost two games and people will try to define us by those two games but what Stuart has built is more than that.
"This whole campaign and the three and a half years of his leadership has been built on rock solid foundations. He has done marvellous things for this country and this rugby team."
Japan coach Eddie Jones weighed into the debate in his Daily Mail column, saying Lancaster was entitled to a "proper review". But that did not stop the Australian lining himself up as a possible replacement.
"If England approached me, would I listen to them? Of course I would, but whether the RFU part ways with Stuart Lancaster is a big and difficult decision," he wrote.
England have already felt the reverberations of becoming the first former winners to go out in the pool stage when they slumped to eighth in the latest world rankings, equalling their lowest ever position.
There could also be repercussions from governing body World Rugby who said in a statement on Monday they were probing an alleged "breach of the match-day communications protocol" by the England coaching team during the 33-13 loss to Australia.
MIXED FORTUNES
There was good and bad news on Monday for the Wallabies, whose game against Wales on Saturday will decide who finishes top of Pool A.
Australia winger Rob Horne's shoulder injury is not as bad as feared but they could lose loose forward Michael Hooper who has been cited for charging into a ruck shoulder first against England.
Samoans Alesana Tuilagi and Faifili Levave were also cited for foul play during the loss to Japan on Saturday and could miss their country's final Pool B match against Scotland.
Talk of South Africa's demise after a shock defeat by Japan in their opening game has dissipated after wins over Samoa and Scotland and coach Heyneke Meyer played it safe by naming a strong side for the Pool B finale against the United States on Wednesday.
With a victory still required to ensure they reach the quarter-finals Meyer has made just two changes, both due to injuries, to his starting lineup.
Tighthead prop Frans Malherbe replaces Jannie du Plessis for his first start of the year, while speedster Lwazi Mvovo comes in for JP Pietersen, with Bryan Habana moving over to the right wing.
The two matches on Tuesday offer four teams the chance of winning their first match of the tournament.
Fiji, after spirited performances in defeat by England, Australia and Wales in Pool A, start as hot favourites to beat Uruguay while Canada face Romania in Pool D.
(Editing by Ken Ferris)
