Peter Tauber, secretary-general of German Chancellor Angela Merkel's conservative CDU party, will step down from his post for health reasons, party sources said Sunday.
Tauber, 43, will announce his decision on Monday, the sources said, with a successor to be named at an extraordinary party congress on February 26.
Although Tauber is seen as a close associate of Merkel's, infighting within the CDU (Christian Democratic Union) led the chancellor to designate another party stalwart to draft the party's electoral platform last year.
Tauber's intestinal illness prevented him from taking part in the protracted negotiations to form a government following last September's inconclusive elections.
He underwent surgery for his condition last month.
The CDU and the Social Democrats (SPD), both weakened by the elections, finally reluctantly renewed their left-right "grand coalition" or "GroKo" last week.
The deal is still subject to a ballot by the SPD's deeply divided base of 470,000 rank-and file members.
Some within the CDU have criticised the deal, which saw the SPD clinch the finance portfolio, as too generous.