"It is just the one change. We always review the entire match squad after a game but we are trying to achieve some consistency in selection for this team. We have identified problems and we have spent the week correcting them.
"We are still growing into the way we want to play and momentary lapses against Australia on Saturday meant things broke down slightly."
The 28-14 defeat by Australia highlighted how much England needed more of a presence around the fringes and Haskell will provide extra bulk alongside Sheridan, whose size will be vital in the scrum.
The eighth Wasps player in the squad, Haskell's team-mate Simon Shaw, will have to win his 50th cap from the replacements' bench. He is joined there by Leicester No8 Jordan Crane, who takes over from Bath's Michael Lipman.
Johnson also dismissed claims by the Springboks management that their players will find motivation a problem at Twickenham on Saturday.
Coach Peter de Villiers had suggested that his players were thinking more about the "beach" than rugby, but the England team manager said: "Yes, they have been away from home a long time but that's rugby. They will want to finish on a high by beating England at Twickenham."
