Colin Southgate, chairman of Whitehead Mann which is advised by Close Brothers Corporate Finance, said that as a result of losing several US staff the firm has significantly reduced its US operations and written off associated goodwill in the US market.
Anna Mann, the firm's founder and once its best business generator, left in March and has no involvement with the business.
Paul Jones, an analyst at Numis Securities, said the Whitehead Mann brand name was dependent on its key staff and would be seriously devalued without them.
He said: "With a number of departures at Whitehead Mann we remain sceptical that a bid at current levels will materialise in the short term, given the need to quantify exactly what any purchaser would be buying."
Whitehead Mann reported a pre-tax loss of 8.9m (€12.7m) in the six months to September 30 against a profit of 3.6m last time. Turnover fell from 30.3m to 26.9m and the dividend halved to 1.5p.
The group's shares jumped 23% to 167p following last week's announcement that the firm had received "a number of approaches" which may or may not lead to an offer.
At 12.15 GMT today, they were down 3.8% at 153p valuing the firm at 44m.
A source close to the talks said Heidrick & Struggles and Korn/Ferry International, two US headhunting groups, have held discussions.
Both Whitehead Mann and Close Brothers declined to comment further.
In June, the firm faced a barrage of criticism over the short-lived appointment of Sir Ian Prosser as chairman-elect of J Sainsbury, the troubled UK supermarket.
In July, Peter Bracken, Whitehead Mann's former head of communications, was found guilty of insider trading.
Last month firm issued a profit warning after losing its top team of financial services headhunters in New York.