Star bond fund manager Bill Gross of Janus Group, like many others, is concerned about the recent turmoil in global financial markets.

With banks hobbled in their market activity by more stringent regulation since the 2008 financial crisis, a liquidity crunch represents a real danger, he writes in a commentary.

And what could spark such a crisis?

1. "A central bank mistake leading to lower bond prices and a stronger dollar," Gross writes. The Federal Reserve may begin raising interest rates in September.
2. Greece. A default/restructuring will lead to more worries for weaker eurozone economies, he says.
3. China. "It's the mystery meat of economic sandwiches: you never know what’s in there," Gross explains. "Credit has expanded more rapidly in recent years than any major economy in history, a sure warning sign."
4. Emerging markets crisis.
5. Geopolitical risks.
6. "A butterfly’s wing. Chaos theory suggests that a small change in non-linear systems could result in large changes elsewhere," Gross writes. "Call this kooky, but in a levered financial system, small changes can upset the status quo."

So given the volatility in global markets, how should we U.S. investors react, sell all our financial assets and head for the hills? Not quite, says financial author and former banker Jeremy Josse.

"The big question for your average investor is how do you react to [the Greek] puzzle? What portfolio adjustments do you make?" he writes on TheStreet.com. "Well, in spite of some short term turbulence, the best answer is: it perhaps no longer matters very much."

It matters a great deal to the Greeks, of course. "But for most U.S. (or even non-Greek European) investors, Greece has already been significantly taken out of the financial equation," Josse explains. Only $14 billion of Greece's $350 billion debt is owed to U.S. banks.

He points out that banks in general have vastly curbed their lending to Greece over the past few years, and investors have largely steered clear of Greek stocks and bonds.

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