Former NYSE CEO Dick Grasso says he’s asking the $4 trillion question that many other financial experts and economic pundits aren’t posing.

Grasso told CNBC on Wednesday that he worries about how the central bank plans to reduce its $4.4 trillion balance sheet.

"How are you going to do that in the context of everyone else in the world stimulating [and] lowering rates — applying, if you will, the type of stimulus we applied."

The total assets of the Fed have increased from about $869 billion in August 2007, during three rounds of quantitative easing bond purchases that started in November 2008 in an effort to support the economy and combat the effects of the financial crisis, CNBC reported.

"Four trillion is unprecedented, but to shrink it by two-thirds you don't have a comparable period in our history," Grasso said.

Meanwhile, U.S. monetary authorities ought to consider making the central bank’s big balance sheet a permanent fixture, said former Federal Reserve Chairman Ben Bernanke.

“I wonder if the case for keeping the balance sheet somewhat larger than before the crisis has been adequately explored,” Bernanke recently said in prepared remarks to an event at the International Monetary Fund in Washington.

“Indeed, most other major central banks have permanently large balance sheets and are able to implement monetary policy without problems.”

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