Wulff will face questions from Germany's two main state broadcasters, ARD and ZDF.
"The president will give an interview during the course of the day, which will be aired in the evening," ZDF announced on Twitter.
Chancellor Angela Merkel, who has remained silent on the latest allegations, is expecting Wulff to offer his own account of the scandal during the interview.
"The chancellor is expecting him to explain himself," her deputy spokesman Georg Streiter said Wednesday.
Wulff has remained conspicuously silent since allegations emerged earlier this week that he threatened two newspaper editors, of Bild and Die Welt, if they ran stories about a personal loan he took out in 2008.
But though he retained support from politicians as he faced initial allegations of impropriety in December, several party leaders began casting doubt on his suitability for the presidential office on Tuesday and Wednesday.
"No-one would wish for the second resignation of a president within two years," Sigmar Gabriel, head of the centre-left Social Democratic Party, wrote on his Facebook page Wednesday. "But no-one would want a president who gives the impression he is not fit for his office, either politically or in his style.”
Green Party co-chair Claudia Roth told the Süddeutsche Zeitung newspaper that Wulff would likely be a “very weak president” even if he managed to ride things out and called on him to consider whether he should remain in office.
She also demanded that Chancellor Angela Merkel address the issue publicly.
Merkel said several weeks ago that she supported Wulff, although she has declined to comment on the matter recently, as have other leading members of the centre-right Christian Democratic Union, which Wulff is a member of.
Adding to the pressure was a report that Berlin prosecutors were considering whether to open a criminal investigation into the president, though Wulff retains criminal immunity while in office.
In December, it emerged that Wulff failed to reveal a private €500,000 loan he took out with the wife of a businessman when he was state premier of Lower Saxony in 2008.
Charges later emerged that he had received a preferential rate on a replacement loan with a bank in the state of Baden-Württemberg, and may have helped an event planner friend get government business.
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But the biggest blow may be the charges that emerged this week that he had threatened journalists who exposed the scandal with “war” in a voice mail message.
Although such an outcome would be extremely unlikely, Wulff could be impeached by the Bundestag if the parliament determines he has violated the law.