Fisher, who left the COI in July, said M&S risked taking its eye off customer needs by demoting the post previously held by Alan McWalter.
She said: "The problems M&S suffered boiled down to the fact that it lost touch with its consumers. Marketing is the discipline that brings firms closer to their consumers. With no one at board level to wave the flag for the consumer, M&S is taking a huge gamble."
Fisher's comments come as M&S is understood to be struggling to fill the role, now relegated to a place on the group's operating committee.
BBC marketer Jane Frost is believed to have turned it down. It also emerged this week that, contrary to speculation, Frost will not be joining the Chartered Institute of Marketing as chief executive.