Marsh is expected to reveal the impact of the Spitzer investigation on its revenues to investors today.
The world's largest broker has come under scrutiny from the New York attorney general, Eliot Spitzer.
Spitzer alleges Marsh steered clients toward insurers with which it had valuable pay-off agreements called contingent commissions. It is also alleged to have sought rigged bids that made the practice appear competitive.
Since the investigation was announced on Thursday, shares in Marsh & McLennan have lost more than a third in value, almost $9bn.
