The Australian fell on his head and shoulder after coming into contact with the South African in Cape Town last Saturday during a match won 32-30 by the Sydney-based franchise.
Wallaby Foley recovered unscathed from the collision and his conversion in the final minute of a Michael Hooper try won the match for the Waratahs.
Zas will miss a South African inter-provincial match next weekend and a Super Rugby fixture against the Tokyo-based Sunwolves in Singapore on May 14.