The head of GM's
Michael Richards, 52, was named general manager of Buick GMC on December 1, the same day Whitacre made the surprise announcement that CEO Fritz Henderson had resigned.
Richards was the first top executive hired from outside the company after GM's bankruptcy earlier this year.
Michael Richards has elected to leave GM to pursue other opportunities, General Motors said in a statement attributed to Susan Docherty, recently named chief of the automaker's U.S. sales and marketing.
Richards, a 27-year veteran of Ford Motor Co
Richards could not be immediately reached for comment.
A person familiar with the situation said Richards opted to leave GM after the sudden change Lutz's role. Lutz helped recruit him and introduced him to reporters and analysts at the Los Angeles auto show last week.
Richards told GM he was leaving on Wednesday, the same day the company announced that the head of the mass-market Chevy brand, Brent Dewar, 54, was being replaced.
Dewar, a 31-year veteran of GM, had headed the Chevy brand since July. Dewar is being succeeded by James Campbell, 45, previously the head of Chevrolet's fleet sales operations.
The Buick and GMC brands will be headed by Brian Sweeney on an interim basis, a GM spokesman said. The automaker said it would consider internal and external candidates as a permanent replacement. Sweeney has been general sales manager for Buick GMC.
Whitacre has taken charge as acting CEO at GM while the company searches for a permanent successor to Henderson.
The automaker, which came through bankruptcy in July after taking $50 billion in U.S. government aid, is also on the verge of hiring a new chief financial officer.
(Reporting by Bernie Woodall; editing by John Wallace)