Shares of UnitedHealth Group slumped 6% in premarket trading Thursday on a report that the U.S. Department of Justice is investigating the embattled health insurance provider for possible criminal Medicare fraud.

Stephen Hemsley ran UnitedHealth Group for more than a decade. It's a different company after four years with Andrew Witty in charge.

May 13 (UPI) -- UnitedHealth Group announced Tuesday CEO Andrew Witty will step down, citing "personal reasons." Witty will leave the role of CEO and be replaced by Stephen J. Hemsley, effective immediately.

Andrew Witty has resigned as chief executive of US health conglomerate UnitedHealth Group, as the company pulled its financial forecasts for 2025, adding to a sense of crisis after a turbulent period.

Witty’s departure was surprising, though it follows a sharp downturn in the healthcare juggernaut’s financial outlook. He is being replaced by Stephen Hemsley, the chair of UnitedHealth’s board and a previous chief executive.

UnitedHealth Group CEO Stephen Hemsley, who replaced Andrew Witty, said he has the right strategy in place “for the era ahead.”