Investors should cut risk heading into 2016 as central banks trying to pump up their respective economies make losing bets, bond guru Bill Gross says.

Institutions like the Federal Reserve and the European Central Bank are like "casinos" that create money instead of chips "they'll never have to redeem," said Gross, founder of bond giant Pimco who now runs the $1.4 billion Janus Global Unconstrained Fund for Janus Capital.

Furthering the gambling analogy, he said central bankers are using a familiar ploy — doubling down on losing bets until they break even.

In the years after the financial crisis, the Fed, the ECB, the Bank of Japan and other global counterparts have created money used to buy various assets. Financial markets have climbed as a result, but real economic growth has been more elusive.

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"How long can this keep going on? Well, theoretically as long as there are financial assets (including stocks) to buy," Gross said in his monthly letter to clients. "Practically the limit is really the value of the central bank's base currency. If investors lose faith in a reasonable range for a country's currency, then inflation will quickly hit targets and then some."

"No rational observer would call these post-Lehman efforts a success," he added, referring to the collapse of investment bank Lehman Brothers on Sept. 15, 2008, the event many consider to be the seminal event of the financial crisis.