Caparello, a former WBO title challenger, failed a test for elevated testosterone levels and was set to be pulled from the fight against Nyika on 14 September.
The fight at Auckland's Viaduct Event Centre was billed as the feature bout on a card which also included former All Black Liam Messam and New Zealand heavyweight Hemi Ahio, and was set to be the toughest test so far of Nyika's fledgling pro career.
Nyika, an Olympic Games bronze medallist and two time Commonwealth Games gold medallist, has had nine professional fights so far and won eight of them by knockout.
Caparello's resume revealed an impeccable record against Kiwi opponents - with Robert Berridge, Daniel MacKinnon, Reece Papuni, Lance Bryant and Jordan Tai all having been dispatched by the Australian, who has won 32 fights, lost four and drawn one.
Caparello's positive test will leave organisers scrambling to find a new opponent for Nyika.
In statement, event promoters Duco Boxing said they had managed to line-up a "tough, credible and vastly experienced opponent" who could take on Nyika at short notice.
Nyika's new opponent will be announced on Thursday.
