External investigator Freshfields is set to question Franz Beckenbauer about his role in the 2006 World Cup scandal, according to Suddeutsche Zeitung.
Honorary Bayern Munich president Beckenbauer, who was head of the World Cup organising committee, has faced a series of questions over his role in securing the tournament for Germany.
The situation led Wolfgang Niersbach, who was also on the organising committee, to resign his role as president of the German FA (DFB) earlier this month.
Sources have now told Suddeutsche that law firm Freshfields -- hired by the DFB last month to conduct the investigations -- will question Beckenbauer on Tuesday.
In mid-October, German weekly Der Spiegel reported that a slush fund of €6.7 million was set up to buy to the votes of Asian representatives on FIFA's Executive Committee prior to the vote for the host country of the 2006 World Cup in 2000.
The DFB later said that -- with the help of former Adidas CEO Robert Louis-Dreyfus, who died in 2009 -- a €6.7m payment was made to FIFA but insisted it was in 2002 and that only by doing so they were able to secure a financial grant for the organising committee.
When Robert Louis-Dreyfus requested his money back in 2005, it was returned through a FIFA account, and the payment was later falsely declared on the association's tax return.
This has led to tax investigators raiding the DFB headquarters in Frankfurt as well as the private homes of Niersbach, Theo Zwanziger and Horst R. Schmidt, who had all been on the World Cup organising committee, amid suspicions of fraud concerning that €6.7m payment.
Beckenbauer has said he made a "mistake" in making the €6.7m payment to FIFA but denied the cash was used to votes.
Acting DFB presidents Reinhard Rauball and Rainer Koch have also accused the 70-year-old over a contract he apparently agreed with former FIFA Executive Committee member Jack Warner, while the president of the Maltese FA raised questions over a friendly arranged with Bayern prior to the vote.
Beckenbauer addressed the controversy in an interview with Suddeutsche on Saturday, saying he could not recall most of the events, with much of it having taken place over 15 years ago, and added that he signed everything he was asked to sign, and was even willing to put pen to paper on contracts that had not yet been written.
"Whenever my signature was needed, I signed it blind. You might not believe it, but it's like that," he said.
"When I trust someone, I'll sign everything [even if the contract is] blank."
Beckenbauer also criticised Rauball and Koch, claiming they did not reply to a letter in which he offered his help by speaking to the DFB.
Koch said on Facebook that he and Rauball had replied to Beckenbauer and also received confirmation from his office, and that they still are prepared to talk after the former West Germany captain and coach has spoken to the association's external investigators.
"No reason to panic," Koch wrote.