The redemptions were from Pimco's flagship Total Return bond fund, which is the world's largest.
Overall, the fund lost more than 10% of its assets in September.
Pimco said the outflows spiked in the hours after Mr Gross, its co-founder and former chief investment officer, resigned to join rival Janus Capital.
Pimco has been trying to soothe investor concerns and has unveiled three new managers at the Total Return fund.
Pimco moved to reassure investors it could cover the fund withdrawals: "The fund is well positioned to meet potential redemptions, and short-term cash management is an area of expertise and strength at Pimco," the company said in a statement.
Competitors such as Vanguard and DoubleLine Funds have benefited from the problems at Pimco, which has huge holdings in assets such as US Treasury bonds and mortgage-backed securities.
They have attracted hundreds of millions of dollars from Pimco's departing investors, reflecting the sensitivity such funds have to management changes.
Mohammed El-Erian No reason has been given for Mohammed El-Erian's departure from Pimco
Pimco has seen 17 straight months of outflows following a bumpy stretch filled with management shake-ups and increased regulatory scrutiny.
It has seen an increase in redemptions since the US central bank announced plans to end its stimulus programme, known as quantitative easing, last year.
In January, Pimco's co-chief investment officer, Mohamed El-Erian, resigned amid reports of infighting.
Last week it was also revealed one of Pimco's funds is being investigated by the Securities and Exchange Commission to see if it artificially boosted returns.
Pimco is a subsidiary of the German insurer Allianz and has nearly $2tn under management.