The group left the market reeling late yesterday when it announced it had suspended Guillaume Rambourg - one of its most senior hedge fund managers - following consultation with the Financial Services Authority and "pending the outcome of an internal investigation in relation to breaches of internal procedures regarding directing trades".
Its shares plummeted 31% yesterday and opened down more than 10% today before making a tentative recovery.
Gartmore stressed in its statement to the stock exchange that the group was not connected with the recently-reported joint investigation on insider dealing by the FSA and the Serious Organised Crime Agency (Soca), in which seven people have so far been arrested.
But its shares have already been under pressure amid speculation that it was embroiled in the investigation, down 10% over the past week.
Gartmore added that it had "not identified any information to date which suggests that Gartmore's clients have suffered any loss as a result of these breaches".
The term "directing trades" refers to the ability of a fund manager to choose the broker through which to trade.
They must choose the broker that offers the cheapest price for the stock.
Mr Rambourg's assets will continue to be managed by co-manager Roger Guy while he has been suspended, according to the group.
Gartmore only recently made its stock market debut - a move that is said to have netted Mr Rambourg and Mr Guy multimillion-pound windfalls for their shareholdings.
They also retained sizeable stakes in the firm, with Mr Rambourg said to have a 3.85% holding and Mr Guy a 5.56% stake.
The two managers are seen as key to Gartmore, managing assets of more than 8 billion, or 37% of the group's total assets.
They won Euro Hedge's European fund of the year last year after generating returns of 42% on one of their AlphaGen hedge funds.
"Key person" concerns were raised at the time of the group's stock market listing, given that the two managers are so integral to the firm.