FRANKFURT/HAMBURG - Shares in German truckmaker MAN fell over 4 percent on Tuesday on market talk it may be pressured by major investor Volkswagen to make a bid for Scania.

MAN declined to comment on the talk, which comes amid a series of resignations by top MAN executives that has fueled renewed speculation of a three-way truck alliance among MAN, VW and VW's Swedish unit Scania.

MAN faces a leadership vacuum after Chief Executive Hakan Samuelsson, finance chief Karlheinz Hornung and commercial vehicles boss Anton Weinmann announced within eight days of each other that they were stepping down.

Prosecutors have said none of the men was a target in an investigation into suspected bribery at MAN, but their exodus may clear the way for VW to push through a trucks alliance that could compete with market leaders Daimler and Volvo.

MAN already has a 17.4 percent voting stake in Scania after an abortive takeover bid it launched in 2006 that drove Scania into the arms of Volkswagen, which now has a voting stake of around 71 percent.

VW also holds just under 30 percent in MAN, setting up the chess board for a potential move by VW's powerful chairman, Ferdinand Piech, to create an automotive empire spanning small cars to heavy trucks.

At 1249 GMT shares in MAN were 4.5 percent lower and Scania stock gained 4.5 percent while the DJ Stoxx European Auto Index .SXAP was up 2.8 percent.

There are rumors that MAN is being forced to bid for Scania, a trader in Frankfurt said.

Analysts are mulling whether MAN, which has already bought VW's heavy trucks business in Brazil, could now be pressed into a fresh bid for Scania that would let VW sell its Scania stake.

BHF Bank analyst Aleksej Wunrau said in a note to clients that VW would avoid another acquisition cash-out by bringing its Scania stake into MAN.

This would eliminate the risk of another capital increase at VW, which is poised to issue new preference shares to help finance its purchase of a stake in Porsche's sports car business ahead of a full merger with majority owner Porsche.

Taking MAN shares in payment could give VW a majority stake in MAN, triggering a mandatory bid, he added.

But this could be at the legal minimum that would attract scant take-up, leaving VW in the driver's seat of the new trucks business while conserving cash.

Piech has said the trucks alliance could generate 1 billion euros ($1.51 billion) in synergies and told reporters at the Frankfurt Auto Show in September that a collapse in truck markets posed an opportunity to move forward with his vision.

Everything goes faster in emergencies, he said at the time.

(Reporting by Tyler Sitte and Andrea Lentz in Frankfurt, Joanne Frearson in London and Jan Schwartz in Hamburg; Editing by David Cowell)