Rajan said that being struck off NBIM's list of external managers "could be quite damaging as investment consultants will put them on their 'watch' lists immediately", putting them at increased risk of losing money from other institutional investors.
The oil fund took business away from eight investment houses last year.
This included Thames River, the U.K.-based hedge fund company that lost several senior staff members, including its chief executive, after being acquired by F&C in 2010. F&C was in turn bought by Canada's Bank of Montreal in 2014.
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Black River, the US hedge fund company that was partly spun off from its parent company last year following the closure of several products, was also cut, as well as Sweden's Lancelot Asset Management, Chilean group MBI AGF, and Korea's Truston Asset Management.
The Norwegian oil fund added a number of new investment companies to its roster last year, including Mirabaud, the Swiss asset manager, Brummer & Partners, the Stockholm-based hedge fund outfit, and Sri Lanka-based Lynear Wealth Management.
Michael Maduell, president of the Sovereign Wealth Fund Institute, a US-based consultancy, said: "Norway's sovereign fund hires all types of managers, large, medium and emerging. For smaller managers, it is a great opportunity to land larger mandates with other asset owners."
The Norwegian oil fund declined to comment on the changes to its roster of asset managers.