"When one leaves a country, it abandons all the attributes that the membership there provides,” the Spanish top diplomat said, as quoted by El Pais.
He referred to the examples of the Latin American states, whose population lost Spanish nationality after obtaining independence.
"If they seek an independent state of seven million citizens, all of them with Spanish nationality, it is a bit absurd,” Garcia-Margallo stressed.
Catalonia has long sought independence from Spain, accusing Madrid of constraining its economic and cultural autonomy and of unfairly distributing resources in the country.
The region is holding regional elections on Sunday. A coalition of pro-independence parties have pledged to set processes in motion for the autonomous region to separate from Spain within 18 months, should they win a majority.