Last year 200m runner Luxolo Adams was withdrawn from the Olympic squad after showing poor form following a lengthy injury that shortened his season. At the time he was replaced in the squad by Wayde van Niekerk.
Five South African sprinters achieved automatic qualifying times in the 100m, but nations can enter a maximum of three in each event.
ASA selected Walaza, Gift Leotlela and Akani Simbine to race in the 100m.
The other two qualifiers are Benjamin Richardson, who was unavailable for selection, and Retshidisitswe Mlenga, who is in the team as a relay only runner.
Allowing Walaza to compete if he’s not fit to do so would be unfair if he were to withdraw too late to allow Mlenga to take his lane.
The three individual 100m competitors are obliged to also race in the 4x100m relay, barring injury. ASA has three other relay only runners as cover — Bradley Nkoana and Shaun Maswanganyi, both members of the team that won Olympic silver in Paris last year, and Abdurahman Karriem.
But the relays coach also has the option of using other athletes, such as 200m sprinters Van Niekerk, Sinesipho Dambile, a member of the 4x100m team that won World Relays gold in China earlier this year, and Naeem Jack.