The Federal Reserve is wrapping up a $600 billion economic stimulus program known as quantitative easing, but it could renew such policy by year's end if the economy is still weak and stocks fall by 10 percent or more, says New York University economist Nouriel Roubini.

Quantitative easing is designed to inject money into banks so they will fuel economic growth and stock-market gains, although critics say it hikes inflation rates and weakens the dollar.

Fed officials says the $600 billion second round of program ends this month.

Don't rule out more, Roubini tells CNBC.

Nouriel Roubini (Getty Images photo)

"Especially because we cannot do another round of fiscal stimulus, the pressure is going to be on the only policy that is available, [that] is another round of quantitative easing," he said.

Roubini, who accurately called the economic collapse well before 2008, says there are too many potholes in the economy's road to recovery.

"You have the problems of rising oil prices, of [a] weak labor market, of housing double dipping, the fiscal problem in the state and local governments, the facts of the federal deficit problem," Roubini says.

"All these things imply that economic weakness could persist in the second half of the year."

Fed officials, however, are sticking to their guns.

They say the first and second rounds of quantitative easing have pumped plenty of money into the financial system and that any more could threaten to hike inflation rates.

"There's about $1.5 trillion of what we call excess reserves in the banking system: they're just sitting there, they're not creating inflation, at least not yet. But they do have the potential to do that," Fed Federal Reserve Bank of Philadelphia President Charles Plosser tells the BBC Radio.