For all the concern that Wall Street's shrinking balance sheets will fuel a liquidity crisis when investors flee credit markets, Citigroup Inc. strategist Stephen Antczak says investors may be overlooking an even bigger catalyst.

The size of the U.S. corporate-bond market has ballooned by $3.7 trillion during the past decade, yet almost all of that growth is concentrated in the hands of three types of buyers: mutual funds, foreign investors and insurance companies, according to Citigroup. That combination could lead to more selling than the market can absorb when the Federal Reserve raises interest rates for the first time since 2006, Antczak said.

"All the money is going to the same place, and when something adversely impacts one, chances are the same factor adversely impacts everyone else, and there's nobody there to take the other side," Antczak said in a telephone interview. "We used to have 23 types of investors in the market. Now we have three. In my mind, that's the key driver."