Despite being 44, Botha, also known as the White Buffalo, is a step up in class for New Zealand heavyweight champion Williams. At the very least he should be able to take a punch, which hasn't always been the case with Williams' opponents.
Botha's record is 48 wins, eight losses, three draws, compared with the undefeated Williams' five wins.
"His experience speaks for itself," said Williams, who is in Auckland seeing family.
"For me in a boxing sense I need to take fights like this to move up.
"It's definitely going to put my name out there internationally if I win because it's for a WBA international belt."
The fight was originally scheduled for last year but was put back due to Williams' chest injury suffered while playing for his Panasonic club in Japan. APNZ