BERLIN (Reuters) - Support for Germany's Free Democrats (FDP), junior partners in Angela Merkel's centre-right coalition, has fallen to its lowest level in nearly a year, a poll showed on Wednesday, complicating the chancellor's hopes of winning re-election in September.
The Forsa poll gave Merkel's conservatives 42 percent, their best result since the last federal election in 2009 but not enough to govern alone, meaning she may have to forge a post-election deal with one of the opposition parties.
The survey gave the liberal FDP - a veteran participant in German coalitions since World War Two - just 2 percent, down from 4 percent in the previous Forsa poll and below the 5 percent threshold for entering parliament.
It is the FDP's worst result in a Forsa survey since last February and comes amid mounting speculation that the party will replace its ineffectual leader Philipp Roesler, especially if it fares badly in a regional election due later this month.
The poll of 1,503 people was conducted on January 2-4, just before a weekend FDP conference that the media said failed to dispel doubts about the party's direction and appeal to voters.
The survey gave the main opposition Social Democrats (SPD) 25 percent and the Greens, their favoured coalition partner, 15 percent. The only other party seen entering parliament is the Left Party, on 9 percent.
The SPD has suffered from a string of gaffes by its candidate to replace Merkel, feisty former finance minister Peer Steinbrueck.
By contrast, Merkel's conservatives are benefiting from a still relatively strong economy, hopes that the euro zone crisis may be over and a perception that the chancellor stands up for German interests abroad.
Political commentators say Merkel may try to forge a 'grand coalition' with the SPD if the FDP fails to re-enter parliament after the election. She led such a coalition with the SPD from 2005 to 2009.
Writing by Gareth Jones; Editing by Stephen Brown