Cupido’s club Stellenbosch FC confirmed the move after Foster had been an injury-doubt following Friday’s 0-0 draw with Zimbabwe in Durban.
Cupido, 24, has five caps after making his debut in the 2024 COSAFA Cup, and scored his first international goal in June’s 2-0 friendly win over Mozambique.
The absence of Foster makes it likely that Orlando Pirates striker Evidence Makgopa will start the game against Rwanda, with Cupido an option off the bench.
South Africa must beat Rwanda to have a chance of qualifying for the global finals in the United States, Mexico and Canada.
They must then hope that Benin do not beat Nigeria in Uyo at the same time.
A draw for Benin would mean Bafana Bafana need victory by two clear goals to overtake the west African nation at the top of their pool.
South Africa had already drafted in another Stellenbosch player, centre-back Thabo Moloisane, as a replacement for the suspended Mbekezeli Mbokazi.