BERLIN (Reuters) - German carmaker Daimler (>> Daimler AG) is grappling with the surprise resignation on Tuesday of long-standing executive board member Andreas Renschler who had been rumored as a potential candidate to succeed Chief Executive Dieter Zetsche.

Renschler, production chief at the Mercedes-Benz luxury-car division, is leaving the company "for personal reasons" with immediate effect, Daimler said in a statement.

He'll be replaced by Markus Schaefer, head of production planning at Mercedes passenger cars who used to run the carmaker's Tuscaloosa, Alabama-based plant and has over 20 years of experience in car-assembly, Daimler said.

"I very much regret that he (Renschler) is leaving the company for personal reasons," Daimler Chief Executive Dieter Zetsche said, noting Renschler's contribution to last year's launch of the Mercedes flagship S-Class sedan.

Successor Schaefer's "broad knowledge of our production business and international experience gathered from his positions in the United States give him excellent qualifications for this job," the CEO said.

A company spokesman said Renschler left for purely personal reasons, ruling out that possible dissent on policies within the management board or health-related matters played any role.

Daimler narrowed a sales gap with its German premium-car rivals BMW (>> Bayerische Motoren Werke AG) and Volkswagen's (>> Volkswagen AG) Audi last year, thanks to a spate of redesigned compact vehicles. The Stuttgart-based manufacturer dropped to third place in the luxury-sales race behind Audi in 2011.

Renschler, who became Mercedes production chief last April after running Daimler Trucks for more than eight years, had pledged to carry on with the efficiency program initiated by his predecessor Wolfgang Bernhard.

(Reporting by Andreas Cremer, editing by David Evans)

Stocks treated in this article : Bayerische Motoren Werke AG, Daimler AG, Volkswagen AG