Bill Gross, who manages the world's biggest bond fund, said the U.S. Treasury will likely be forced to buy as much as $30 billion of preferred shares in both Fannie Mae and Freddie Mac to help shore up their capital.

"By the end of the third quarter, the preferred stock in Fannie and Freddie will be issued, the Treasury will have bought it," Pacific Investment Management Co.'s Gross said yesterday in an interview with Bloomberg Television.

"We'll be on our way toward a joint Treasury/agency combination."

Gross' Total Return fund has returned 5.5 percent annually over the past five years, beating 86 percent of its peers in the government and corporate bond fund category as of Tuesday, according to Bloomberg data.

Pimco, a unit of Allianz SE based in Munich, Germany, has $830 billion of assets under management.