German Health Minister Philipp Roesler, designated leader of the government's Free Democrat (FDP) junior coalition partner, is likely to take over the post of Economy Minister, a source in his party said on Monday.

Other party sources said there was a strong possibility current economy minister Rainer Bruederle would become FDP parliamentary floor leader as part of a shakeup designed to revive the sinking popularity of the centrist party.

Bruederle's appointment would be confirmed at a party meeting on Tuesday.

It would help clear the way for the election of Roesler as FDP head at a Saturday congress in the Baltic city of Rostock that could expose stark divisions in the party.

Roesler would succeed Foreign Minister Guido Westerwelle, who stepped down after regional elections revealed slumping electoral support for a party that frequently served as kingmaker in post-war German politics.

The FDP would lay claim to the Economy Ministry under the coalition agreement with Angela Merkel's centre-right Christian Democratic Union.