As a result of the positive test, England head coach Eddie Jones and attack coach Simon Amor have also begun a period of quarantine as close contacts to Proudfoot.
It means that when England’s players gather at St George’s Park for training next Wednesday, that neither Jones, Amor nor Proudfoot will be in attendance.
But the RFU said the pair would be available to join the group the following day under Government regulations.
It is the latest setback to England’s Six Nations preparations after it was revealed earlier this week that another member of England’s coaching staff, Jason Ryles, would not be joining up with the squad from his native Australia because of travel fears over Covid-19.
In the absence of Jones, Amor and Proudfoot, it is thought that John Mitchell, the only senior coaching figure not currently having to isolate, will take charge.
England’s training squad is expected to be announced on Friday.