Daimler's supervisory board is due to sign off on the extension to the end of 2018 at a meeting on February 6, weekly Der Spiegel said on Sunday, citing no sources.

A spokesman for Daimler said the company generally did not comment on matters concerning the supervisory board.

A source had told Reuters in September that Daimler was expected to extend Zetsche's contract by three years to 2016.

The news came as analysts warned that investors were growing increasingly concerned about Daimler's inability to close the performance gap with rivals Audi and BMW.