The controversial former church leader "enriched himself substantially" at the expense of his Foundation for Peace and Justice, according to the conclusions of the inquiry, conducted by a Johannesburg legal firm for the Danish donor organisation, Danchurch Aid.
Mr Boesak's UN posting was put on ice by President Nelson Mandela last month pending the conclusion of the inquiry. A presidential spokesman said a decision would be taken before the end of the week.
Mr Boesak was already reeling from allegations that his foundation misused funds donated by the American singer, Paul Simon, to a charity for child victims of apartheid. The Archbishop of Cape Town, Desmond Tutu, said on Monday that he had called in police after preliminary investigations had shown no record of 423,000 rand (£76,500) donated by Simon to the Children's Trust, administered by the Foundation for Peace and Justice.
Late last year, Danchurch Aid and two other funding organisations in Sweden and Norway engaged a Johannesburg legal firm to examine the use of 2.7m rand donated to Mr Boesak's foundation. The report hit out at the foundation's trustees, calling the "cavalier and reckless fashion" in which they carried out their duties "astounding". It quoted one trustee, the Rev Pierre van den Heever, as acknowledging: "We buggered it up."
The foundation director, Freddy Steenkamp, who has already admitted taking a loan of 800,000 rand, had "committed serious criminal offences". Mr Boesak, the report said, "has enriched himself substantially at the expense of the foundation". His explanation to date is that he did not know how his financial affairs were being conducted by Mr Steenkamp.