Dowson is suffering from a tight hamstring after Thursday's training session and the medical staff decided to withdraw him from the match 22, England said in a statement.
Dowson's place amongst the replacements is taken by the uncapped, New Zealand-born Thomas Waldrom, who was the man-of-the-match in the midweek victory over the Southern Barbarians in Kimberley.
The 29-year-old former Hurricanes and Crusaders player showed exactly the sort of power and physicality that England will need against the Springboks if they are to keep the three-test series alive on Saturday, after losing the first 22-17 in Durban last weekend.
