Hooker blow for Boks
Lions hooker Malcolm Marx, rated as the premier hooker in the world, has been ruled out for six weeks - making him unavailable for the Tests against Wales and England.
Marx has a high-grade hamstring tendon tear.
He does not require surgery and is expected to be sidelined for at least six weeks.
Marx was injured in the Super Rugby match against the Hurricanes in Wellington last weekend.
The 23-year-old made his debut for the Springboks against the All Blacks on 17 September 2016.
He has scored three tries in his 14 Tests and was rated one of the certainties to feature in Erasmus' first Test series.
The Boks tackle Wales in the American capital, Washington, on June 2, before taking on England in a three-Test series on home soil - Johannesburg (June 9), Bloemfontein (June 16) and Cape Town (June 23).