Germany's Social Democratic Party (SPD) leader Martin Schulz would not be the right replacement for Chancellor Angela Merkel because of his choice to prioritize the needs of Greek communists over German taxpayers, Germany's deputy finance minister Jens Spahn told CNBC on Wednesday.
"(Schulz) is part of the political elite in Brussels and Berlin but he tries to shape himself as someone from outside and so far it seems to work but of course we have to tackle him on this and to ask him about his positions in the past," Spahn told CNBC on Wednesday.
"He was always a better friend to the communists in Athens than to the German taxpayers and that for example is an issue we will bring up," he added.
SPD party delegates officially backed Schulz with 100 percent of the vote on Sunday as they nominated the former European Parliament president as their new leader.
Schulz's approval ratings have rocketed skywards in recent months and the center-left candidate now finds himself as the political frontrunner to become Germany's new premier, according to the latest opinion polls.
Merkel and Spahn's Chrisitan Democratic Union (CDU) were accused of showing signs of nervousness in response to the deputy finance minister's remarks on Wednesday, an SPD spokesperson told CNBC via email.
"It's obvious that the CDU is quite nervous about the outstanding performance of Martin Schulz. Spahn's comments are hilarious at best. Our campaign will be about policy and not about personal attacks," Niels Annen, SPD foreign affairs spokesperson, told CNBC via email.
Schulz has built a political reputation in Brussels and Berlin as a straight-talking champion of Europe who has campaigned for the bloc's best-performing economies to help ailing euro area members, such as Greece.
The SPD leader has yet to outline his campaign policies, given the embryonic stage of the election campaign, and Spahn argued Schulz's "establishment" past could come back to haunt him later in the year. German voters head to the polls on September 24.
A potential headache for Schulz could prove to be that while he has historically been in favor of Germany doing more to help Athens, a stark contrast to Merkel's stance, most citizens do not appear to support this concept.
Spahn suggested that economically Berlin is in better shape than it has been for decades under Merkel's tenure and while the conservative government plans to emphasize this during the campaign, he told CNBC the political campaign is likely to revolve around immigration concerns.
"The question of homeland security… How safe is it actually to walk through our train stations? That's a big issue for many many people in Germany and so if we talk about this and we have two parties with different positions on that, that's going to be a good campaigning year," Spahn predicted.