Investec Asset Management has moved to limit inflows into its award-winning UK Smaller Companies fund, run by Phil Rodrigs.
The group will stem inflows in order to protect the performance of the fund, after it swelled to nearly £500m in size.
The portfolio, which currently has £460m under management, has grown sharply since last summer, having been just £308m in size last August.
While Investec has not soft-closed the portfolio, it is understood to have stopped promoting the fund, and is discouraging new investment.
Under Rodrigs' stewardship, the fund - which uses the group's 4Factor process - has shot to the top of the UK Smaller Companies sector, rivalling established names including Standard Life Investments' Harry Nimmo.
In the last year alone, Rodrigs (pictured), delivered 21.4% to investors, well above the IMA UK Smaller Companies sector average return of 16.2%, and over three years he has returned 62.8%, versus an average return of 42.9%.
Rodrigs' success has seen him win a number of awards, including the coveted Outstanding Rising Talent award at the Morningstar OBSR awards this year.
An Investec spokesperson said: "We are absolutely focused on sustaining our leading performance track record, by maintaining our focus on being a core small-cap fund.
"We have taken the decision not to fundamentally change the way in which the fund is managed, and therefore the only way to ensure that we can continue with the current cores small-cap approach is to manage flows [in future]."
An eventful week for the trade body
Claims PIMCO refused to pay 2014 bonus
Firms honoured at gala dinner
Canada Life International, Schroders, and Old Mutual International among winners
Stuck in 2% growth phase