Erasmus has hinted his final 31-man selection for the tournament in Japan, which will be announced on August 26, will be drawn from the players in camp this week with the remainder on stand-by in case of injury.
The players released from the group that defeated Argentina 24-18 in a one-off test in Pretoria on Saturday are prop Wilco Louw, hooker Scarra Ntubeni, loose forward Marco van Staden and utility back Dillyn Leyds.
The final squad of 31, as well as six stand-by players, will be selected from those in camp, as well as loose forward Marcell Coetzee who has not travelled after leaving the field with concussion at Loftus Versfeld.
Apart from team building exercises, the SA coaches and conditioning staff will put the players through field sessions and a series of technical activities.
There are no newcomers to the squad from those that helped the Springboks lift the Rugby Championship title for the first time in a decade earlier this month.
They have a final warm-up fixture against Japan on September 6 before opening their World Cup campaign against New Zealand 15 days later in Yokohama.
Forwards: Schalk Brits, Lood de Jager, Thomas du Toit, Pieter-Steph du Toit, Rynhardt Elstadt, Eben Etzebeth, Lizo Gqoboka, Steven Kitshoff, Vincent Koch, Siya Kolisi, Francois Louw, Frans Malherbe, Malcolm Marx, Bongi Mbonambi, Tendai Mtawarira, Franco Mostert, Trevor Nyakane, Marvin Orie, Kwagga Smith, RG Snyman, Duane Vermeulen.
Backs: Lukhanyo Am, Damian de Allende, Faf de Klerk, Andre Esterhuizen, Warrick Gelant, Elton Jantjies, Herschel Jantjies, Cheslin Kolbe, Jesse Kriel, Makazole Mapimpi, Sbu Nkosi, Willie le Roux, Handre Pollard, Cobus Reinach, Frans Steyn.