New York University economist Nouriel Roubini, who predicted the financial crisis of 2008, doesn't see much evidence of bubbles in the U.S. bond and stock markets.

When it comes to bonds, Roubini is concerned about the strong appreciation of junk bonds, he tells Forbes.

But when it comes to short-term rates, he believes the Fed will essentially keep them at zero until mid-2015, and then they will gradually rise to 4 percent by 2018.

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That slow grind higher limits the chances for a destructive bubble in bonds or housing, Roubini explains. Short-term rates soared to 5.25 percent from 1 percent in just two years during the last Fed tightening cycle, he says.

The stock market also is unlikely to witness a bubble, unless it rises more than 20 percent in each of the next two years, Roubini notes.

The Standard & Poor's 500 Index has generated a total return of 31.6 percent so far this year.

Outside of the junk bond market, Roubini sees "no excesses" in the financial system, and "there is no tipping point in the system as there was in 2007."

Russ Koesterich, global chief investment strategist at BlackRock, agrees with Roubini about the absence of a bubble in the stock market.

"Part of it is valuation and the other part is sentiment," Koesterich tells USA Today. "When you look at the measures of sentiment, they tell you that people are optimistic. But valuations and sentiment have been more extended and more euphoric at past market tops."

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