A vast fiscal fightback to the coronavirus crisis unleashed by eurozone governments could raise questions about capitals' ability to repay debts and revive the threat of countries exiting the single currency, the European Central Bank warned Tuesday.

"Should measures taken at the national or European level be deemed insufficient to preserve debt sustainability, the market assessment of redenomination risk might rise further," the ECB said in its biannual Financial Stability Report.

"Redenomination risk" refers to the danger of some countries quitting the euro -- or the single currency collapsing altogether.