Fixed-income expert Peter Tchir says few investors seem to have a plan for what to do if U.S. stocks and bonds both plunge at the same time.

"The one scenario that I don't know anyone is well-prepared for is if stocks and bonds both fall," Tchir said during Jim Cramer's latest Trading Strategies roundtable for investors.

Tchir said that many investors and Wall Street professionals rely on so-called "risk-parity" strategies that assume stock and bond prices will move in opposite directions. But he said both sometimes fall at the same time.

"That is the one scenario I don't think anyone's very well prepared for -- that bond yields go higher and that drags stocks down," he said. "Where does the liquidity come if people have to sell both?"

Trading Strategies: Sell in May and Go Away?:

Editors' pick: Originally published May 12.

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