He told the news weekly Der Spiegel that the SPD could support a candidate from the opposition conservative Christian Union as long it was a female. "It's time a woman was president," he said. "We will consider any female candidate ... without pre-judgements."
The incumbent, 72-year-old Johannes Rau, leaves office this summer after a five-year mandate, but a federal assembly meets to vote on his successor on May 23.
The presidency is a largely symbolic post involving entertaining heads of state and representing Germany abroad, but offers only an occasional platform to expound on wider social or political concerns.
There has been no shortage of suggestions about who could replace Rau but the debate so far has centred on who does not want the job.
The Christian Union alliance's two leaders, Angela Merkel and her Bavarian colleague Edmund Stoiber, have made it obvious that they see their future in the hurly-burly world of frontline politics.