Mrs Merkel went head-to-head with political rival Martin Schulz on September 3, in what was billed as a one-off live event.
But the SPD leader Mr Schulz has since challenged her to a second debate in a letter, arguing that they failed to address many key issues in the first encounter.
Her Christian Democratic Union (CDU) party rejected the idea, with an official saying: “Angela Merkel enjoyed taking part in the a TV duel.
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“The format worked out well. And she is leaving it at that.”
But now the SPD has savaged the German Chancellor – claiming she has been a coward for backing out of the opprtunity with just a week before citizens go to the polls.
SPD General Secretary Hubertus Heil said: “Merkel has wimped out. This is evidence of a lack of respect for the citizens and the democratic debate.”
While SPD faction leader Thomas Oppermann declared on Twitter, the then SPD Chancellor candidate Gerhard Schröder had to do two TV debates, the former US presidential candidate Barack Obama even three.
Mr Schulz, 61, is a more natural public speaker than Mrs Merkel, 63, but he failed to land a knock-out blow during the debate – partly because the two camps agree on many policy areas.
While it may appear he is calling for the debate to try and have another go, Mr Schulz insists he wants to go head-to-head again as he believes many points that the citizens cared about had not been addressed.
He said: “That is why I wrote a letter to Merkel today and asked her to do another debate with me, so that all these points can be addressed.
“I am amazed that I am writing to the Chancellor personally, and the Adenauer-Haus comments on it and rejects it.”
But the CDU headquarters quickly shit down any notion of an extra debate, saying: “Angela Merkel enjoyed participating in a TV debate, and this format has proven itself, and that is the end of it.”
A survey by Infratest Dimap for ARD television after the debate showed Merkel’s overall performance was viewed as more convincing by 55 per cent, compared to 35 per cent for Schulz.