Saracens pair Mouritz Botha and George Kruis have both been called up for England's senior and Saxons squads respectively.
Botha replaces Northampton Saints' Calum Clark who has a shoulder injury and will join the rest of the training squad today.
As revealed by the Watford Observer 12 days ago, Kruis joins the Saxons squad as injury cover after Wasps' Tom Palmer was ruled out.
It is the talented second row's first call-up to the Saxons having represented England at Under-20 level.
The Saxons' first game is against 02 Ireland Wolfhounds in Galway on Friday, January 25 before their second match against Scotland A at Kingston Park a week later.
England kick off their Six Nations campaign against Scotland on February 2.