The former SPD leader told der Spiegel that his party would not join another grand coalition after the country’s federal election.
Gabriel said a grand coalition after the election would be “pointless” because the SPD party wouldn’t be able to nominate a chancellor as a junior partner. He said he therefore couldn’t foresee the continuation of the Social Democrats working alongside Angela Merkel’s Christian Democrats (CDU) party.
In the German electoral system the largest party in a coalition chooses the Chancellor. Thus the SPD would have to win more votes than Merkel’s CDU party and Bavarian sister party CSU for leader Martin Schulz to get the top job.
Currently in opinion polls the SPD stands at between 22 and 24 percent of the vote, whereas the CDU and CSU are steadily ahead at 37 to 40 percent.
But on Thursday Gabriel denied reports that he no longer believed in the possibility of a victory for Schulz, according to Frankfurter Allgemeine Zeitung.
"Anyone who claims such a thing is talking nonsense," Gabriel claimed in a press release.
The race between Angela Merkel and Schulz is "completely open", he added.
Gabriel pointed out an Allensbach poll from last week which showed that almost half of the voters in Germany were still undecided.
The first live debate between Merkel and Schulz will be aired on television on Sunday.