"The exit from the euro is automatic, the exit from the European Union is implied," Bank of Spain chief Luis Maria Linde said during an event in Madrid today.
He added that the region's banks would lose their access European Central Bank facilities.
Tension is mounting ahead of a regional election on Sunday, which could see Catalan separatists win enough seats to launch a full-blown referendum on independence. Last year, an informal referendum showed more than 80 per cent favoured splitting from Spain.
Scottish voters faced similar warnings of a possible exit from the whole EU, if they had chosen to vote "yes" in the Scottish independence referendum a year ago.
Responding to the likelihood of a freeze on bank deposits if Catalonia declared independence, Linde said while this was highly unlikely, it was a risk.
"It's clear that if there are serious tensions there could be a freeze on deposits as has been seen in Latin America and in Greece. In that respect it's a possibility, a risk."