Pimco fund's outflows hit 10% of net assets in Sept

Pimco's flagship Total Return Fund saw an estimated $23.5 billion in outflows in September, the investment firm said Wednesday.

This means the fund saw a drain of more than 10 percent of its total net assets in one month, according to data from Morningstar, which assessed it at $221.61 billion as of Aug. 31.

Co-founder and longtime Chief Investment Officer Bill Gross announced last week that he would be leaving.

Read More Pimco executives: 'The firm is moving forward'

"Of note, the largest daily outflow occurred on the day of Bill Gross' resignation from the firm, while outflows on the two following days were considerably smaller," the firm said in a press release.

Pimco, which is owned by Allianz , said its Total Return Fund, "is well positioned to meet potential redemptions."

Despite this assessment, rivals such as Vanguard and BlackRock stand to gain from the upheaval at Pimco .

"When you get a star manager like Bill Gross exiting, you cause chaos within the fund family, which is exactly what happened. If I was managing that firm ... even if Bill died, I'd stuff him like 'Weekend at Bernie's' and stick him in a chair. I don't want him going anywhere," said Kevin O'Leary, " Shark Tank " panelist and O'Leary Funds chairman, on CNBC's " Closing Bell ."

Read More Gross fallout: Morningstar downgrades Pimco fund

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