Problems with Greek debt are about to spread to other countries and could infect the US unless the nation tackles its own mounting problems, Pimco's Mohamed El-Erian told CNBC.
About an hour or so after El-Erian spoke, global stocks sold off sharply with major US averages shedding more than 3 percent.
Speaking as Greek austerity measures won enough votes to be approved by parliament, El-Erian offered a stern warning about the potential of the crisis to escalate into something resembling, though not duplicating, the 2008-09 financial crisis.
"We've seen a crisis start in a country—Greece—become regional, impact the whole of the Euro zone and is on the verge of truly going global," said El-Erian, CEO of the world's biggest bond fund.
He said the debt is a "transmission mechanism to go from country to region to global. So we should take this very seriously."
S&P 500 banks fell financials fell nearly 5 percent as investors worried about the financial system freezing up again, similar to what happened when Lehman Brothers collapsed in September 2008.
One trader who spoke on condition of anonymity said fixed-income desks in Europe shut down early for the day and that "European banks are halting lending now."
Similarly, the US faces a debt burden that, while not as large a percentage of gross domestic product as Greece, is approaching that level and could spark major problems domestically.
"We are not Greece. We have more time. But what the Greek crisis tells you is debt and deficits matter," El-Erian said. "The structure of your deficits matter and the US doesn't have much flexibility."
"Don't underestimate how quickly this can happen," he added. "There are structural headwinds out there and we better get our act together before those structural headwinds become overwhelming."
For now, the Greek crisis actually could provide opportunity in the US as assets in riskier European markets are parked in more secure locations.
The downside is that those assets are largely flowing to US bond markets, while stocks are getting pounded by the uncertainty the crisis has sparked.
"What you see is the system slowly starting to have cascading failures. It's like a pipe that you need to be free-flowing and it starts to clog, and that's a concern," El-Erian said. "This is a shock to the system and it's going to have an impact on valuation."