The former President of the European Parliament has seen his standing slip below the psychologically important mark of 30 per cent, according to the results of a survey by Forsa.
The poll, for Stern magazine and broadcaster RTL, had Mr Schulz on just 29 per cent, his lowest standing since his nomination as the party’s leader and a fall of three points since just a week ago.
Meanwhile Angela Merkel, his main rival for the top political job in Germany, has opened up a strong lead on 44 per cent, a rise of one point in seven days and currently looks set to return for a fourth term.
SPD leader Martin Schulz is slipping in the polls
There is no change for the ‘grand coalition’ of Merkel's Christian Democratic Union (CDU) and the Christian Social Union (CSU) as well as the standing of the SPD.
The CDU and the CSU are still at 36 per cent, the Social Democrats come in on 30 per cent.
Mr Schulz performed slightly better in another poll in the past few days with a DeutschlandTrend survey putting the 61-year-old on 36 per cent, but still some 10 points behind Mrs Merkel.
Angela Merkel in pictures
Tue, November 29, 2016
Angela Merkel has served as German Chancellor since 2005 and Leader of the Christian Democratic Union since 2000. We take a look at her political career in pictures.
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German Chancellor Angela Merkel attends the gala for the 200th anniversary of Werner von Siemens on November 29, 2016 at the historic headquarters of Siemens in Berlin
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The poll comes at the same time that the leader of the anti-immigrant Alternative for Germany (AfD) Frauke Petry has announced that she is not interested in being the party’s candidate for the chancellorship in the September election.
In a video message on her Facebook page, she said: "To end all the speculation in this area, I would like to take the opportunity of this video message to declare unambiguously that I am available neither for a lead candidacy on my own nor for participation in a lead team.”
Ms Petry made her surprise decision amidst reports that she was becoming increasingly isolated, after making an official "proposal for the future" that the party should agree on a binding strategy for Germany's national election on September 24.
Chancellor Angela Merkel is riding high in the polls
Frauke Petry will not be the AfD's nomination at the election
The party is hoping to win German parliament seats for the first time this year since it was founded in 2013 – and that year failed to make it past the five percent threshold of votes to make it into the Bundestag.
Currently polling at around 10 per cent, the party looks likely to do just that, with some members of the party predicting that they could become the country's third largest party.
Founded originally as a eurosceptic party, the AfD has veered more to the right in recent years, using anti-immigrant rhetoric to draw support from those displeased by Germany's liberal refugee policies.