Paul O'Donoghue of the University of Chester, who has developed a genetic test to identify pure Scottish wildcats, said extinction is a certainty unless "urgent" conservation measures are put in place.
"Our research shows that the plight of the wildcat is now so serious that unless urgent and targeted conservation activities take place, its extinction due to hybridization is a certainty," he told the BBC.
"Recent estimates suggest that fewer than 100 remain, making it one of the rarest animals in the world."
Large-scale live trapping should be conducted and cats found to be pure-bred wildcats placed in protected areas in the west Scottish Highlands, he said.
Private individuals could be keeping the "very best" wildcats as pets, he said, because in remote and rural parts of the Highlands people often take wildcats that visit their properties into their care.
O'Donoghue urged any such people to come forward to help with the conservation effort.