Former Federal Reserve Vice Chair Stanley Fischer said Tuesday that criticism of the central bank would only cause more uncertainty and accentuate any financial crash that hits the U.S. economy.

In a direct nod to President Donald Trump's continued comments on monetary policy and Fed Chair Jerome Powell, Fischer said the criticism is more serious in this current environment than in previous eras.

"It becomes much more important in the fact that the chairman of the Fed is nominated for only a four-year term — that's what Jay Powell has. And the next nomination, if the president wins the election, would be by the president," he told an audience at the European Central Bank's annual forum in Sintra, Portugal, on Tuesday.

"And that would produce a very different monetary policy. And when that happens there will be a lot of questions to ask," he added, mentioning the liquidity loans that were provided by the U.S. central bank in the 2008 crash.

Fischer, who stepped down in September 2017, said the Fed's lender-of-last-resort function had been reduced by Congress in the Dodd-Frank Wall Street Reform and Consumer Protection Act, and it now had less freedom to make emergency loans in times of financial stress.