UPDATE 1-Third exec resigns at Germany's MAN since Monday

* MAN Commercial Vehicles chief Anton Weinmann to go

* Weinmann leaves effective immediately

* Executive board reduced to just two members soon

* MAN shares down 3.5 percent by 1615 GMT

(Adds details, background)

FRANKFURT/MUNICH, Nov 30 (Reuters) - The third top executive at German truckmaker MAN SE (MANG.DE) has announced his resignation within the past eight days, which will leave the management board almost vacant by the middle of next month.

Anton Weinmann, the head of MAN Commercial Vehicles, will leave the company with immediate effect, the company said on Monday without giving a specific reason for his departure.

"The well-being of the company is my primary focus. This has led me to the conviction that I will back MAN's fresh start on the management level," Weinmann was quoted in a statement as saying.

One week ago Chief Executive Hakan Samuelsson resigned, followed on Friday by the announced departure of finance chief Karlheinz Hornung.

Munich prosecutors said that none of the three is a suspect in a bribery affair under investigation within MAN's core trucks business.

But sources familiar with the matter said Volkswagen (VOWG.DE) Chairman Ferdinand Piech has used the affair to clean house at MAN, a 30 percent unit of VW, in order to push ahead with plans to create a three-way truck alliance that would also include VW unit Scania (SCVb.ST). [ID:nGEE5AN25A]

Once Hornung leaves by Dec. 11 MAN's executive board will consist of just interim CEO Georg Pachta-Reyhofen and personnel chief Joerg Schwitalla.

(Reporting by Christiaan Hetzner and Irene Preisinger; Editing by Michael Shields) ((christiaan.hetzner@thomsonreuters.com; Reuters Messaging: christiaan.hetzner.reuters.com@reuters.net; +49 69 7565 1249))