Investors withdrew about £9m every working day from the Woodford Equity Income fund in April, according to data from Morningstar.
The data showed total outflows from the flagship fund in the month were £187m across 21 working days.
The fund shrank in size by a total of £560m during the month, with poor investment performance contributing to the shrinkage.
The fund had assets of £3.77bn last week, having been more than £10bn in size two years ago.
Over the past three months alone the fund has lost 10 per cent, compared with a gain of 3 per cent for the average fund in the IA UK All Companies sector in the same time period.
Over the past year the Woodford Equity Income fund has lost 17 per cent, compared with a loss of 3 per cent for the sector.
The total assets under management of Woodford Investment Management are now just over £10bn, with about a third of this run for clients of wealth manager St James's Place, which recently reiterated its support for the embattled fund manager.
The Financial Conduct Authority is monitoring the scale of the outflows, something which Woodford Investment Management insists is standard practice for any large fund that is losing assets, and is done to ensure liquidity is being adequately managed.
Liquidity is of particular relevance to investors in Woodford funds, as there has been significant exposure to unquoted stocks, though the fund manager has vowed to exit these by year end.
A representative of Woodford Investment Management said: "We continue to see the widespread enthusiasm for the large, global-facing businesses that dominate the UK stock market, as dangerous from the perspective of valuation risk.
"It is why the fund is - and has been positioned for some time now - towards undervalued stocks woven into the very fabric of the UK economy.
"This broader market malaise in UK quoted domestic stocks has contributed to the fund’s underperformance over the last month.
"However, Neil continues to believe this area of the market, such as house builders and other consumer stocks, are profoundly undervalued and offer long-term potential returns."