The departure of chief investment officer Bill Gross from Pimco will likely cost the money management titan 10 to 30 percent of its assets, say Bernstein Research analysts led by Thomas Seidl.

Pimco had $1.97 trillion of assets under management as of June 30, so that would amount to a loss of $197 billion to $591 billion.

"We would expect a good deal of Pimco clients switching to Janus, simply attracted by the long track record of Bill Gross," Seidl wrote in a commentary obtained by MarketWatch.

Gross, who co-founded Pimco more than 40 years ago, left the firm for Janus Capital Group amid a dispute with other Pimco managers over the firm's future and how to halt the record flow of redemptions from his signature fund, Pimco Total Return.

If Pimco loses 10 percent of its assets, the shares of its parent, Germany's Allianz, may fall 2 percent and 13 percent if Pimco loses 30 percent of its assets, Seidl says.

Allianz shares were down 6 percent at $128.50 Friday afternoon.

Gross' departure shook up the investment world. "I don't shock easily," Vanguard Group founder Jack Bogle told CNBC. "But I was surely shocked when I heard that basically as soon as I got in the office at about 8:30 this morning. I think it's too bad. It's too bad for Pimco."

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