The highly anticipated 42.2km race, set for 17 October, will crown a new female champion before the marathon shifts to its new slot in May next year.
Xaba, coached by Violet Semenya, stunned the nation last year when she set both a course and national record of 2:22:22 to qualify for the world championships.
Despite being invited back by the organisers, the 30-year-old has opted to turn down the R250 000 prize race in favour of competing abroad, saying she wants to broaden her horizons.
"I will be running in places where I don't have a lot have fans and expectations, unlike here in South Africa."
Xaba has tipped former national record holder and two-time Olympian Gerda Steyn to take the honours in her absence.
She believes Steyn has the pedigree to capture the R250 000 prize and ensure the title stays in South Africa.
The Boxer Running Club star also shared insight with SABC Sport on the challenges awaiting runners in the Mother City, warning that the Cape Town Marathon is never easy to conquer.
"The Cape Town Marathon course is great, but the course itself is only challenging, both mentally and physically.
"It's not just a flat course, there are plenty of up-hills, together with the wind, so you have to be stronger and focused," explained Xaba.
The half-marathon and 10km national record holder added that her marathon mark could be under threat if conditions favour the field and athletes stick to their pacing strategy.