There's a 50 percent chance the Federal Reserve will stimulate the economy via unorthodox monetary policy tools although they won't help much, says Laurence Fink, CEO of BlackRock.

The Federal Open Market Committee (FOMC) — the Fed's rate-setting body — will hold its next monetary policy meeting June 19-20.

Market talk says officials may roll out a third round of quantitative easing (QE), which are bond buybacks from banks designed to flood the economy with liquidity and push long-term interest rates down to spur recovery.

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The problem with monetary stimulus, Fink tells CNBC, is that rates are already low and banks awash in liquidity thanks to two past easing rounds.

A third round would just lead to diminishing returns.

"I'm not even sure what QE can do. Is it going to provide more liquidity into the system? Sure. But are we seeing that liquidity transform itself into the lending market? Banks have so much excess money right now. They would like to see more demand," Fink says.

"I don't see what the impact a QE3 would do in terms of the improvement of the economy. I'm pretty dubious on the impact."

When asked whether the Fed would proceed anyway, Fink says "I would say it's at best 50-50."

Since the downturn, the Fed has twice juiced the economy via two rounds of quantitative easing (QE1 and QE2) by buying bonds from banks and pumping the economy with $2.3 trillion in expansionary liquidity in the process.

A dismal May jobs report that showed the economy added a scant 69,000 jobs — far below market forecasts for a gain of 150,000 — is fueling talk the Fed will intervene again.

The economy, meanwhile, grew 1.9 percent in the first quarter, down from a initial estimate of 2.2 percent expansion.

Federal Reserve Vice Chair Janet Yellen has said further easing — often referred to as expanding the Fed's balance sheet — cannot be ruled out.

"There are a number of significant downside risks to the economic outlook, and hence it may well be appropriate to insure against adverse shocks that could push the economy into territory where a self-reinforcing downward spiral of economic weakness would be difficult to arrest," Yellen said in prepared remarks delivered at the Boston Economic Club Dinner.

"Some have expressed concern that a substantial further expansion of the balance sheet could interfere with the Fed's ability to execute a smooth exit from its accommodative policies at the appropriate time. I disagree with this view," Yellen adds.

"The FOMC has tested a variety of tools to ensure that we will be able to raise short-term interest rates when needed while gradually returning the portfolio to a more normal size and composition."

Quantitative easing tends to spark debate.

Supporters say the policy steers the country away from deflationary decline, while critics dub the tool as printing money out of thin air and plants the seeds for inflation down the road.

Editor's Note: You Deserve to Know What Obama and Bernanke Are Hiding From Americans