Independent TD Mick Wallace has said he does not feel any purpose would be served by appearing before the Public Accounts Committee to answer questions about his NAMA claims.
PAC is this week expected to discuss claims that millions of pounds linked to the sale of NAMA properties in Northern Ireland had been "reportedly earmarked for a Northern Ireland politician or political party".
In the Dáil on 2 July, Mr Wallace made a number of serious allegations about the deal, which he said was called Project Eagle.
In a letter seen by RTÉ News, Mr Wallace tells the clerk of the committee that his appearance would not serve any purpose.
He said what was needed was an independent inquiry to investigate the entire NAMA operation.
Last year a US investment company, Cerberus Capital Management, bought a NAMA portfolio of Northern Ireland-based debtors.
It had a book value of £4.5bn. The purchase price was not disclosed but NAMA said at the time it was the biggest single transaction in the agency's history.
Mr Wallace claimed a routine audit showed £7m in funding ended up in an Isle of Man bank account.
He said the money was "reportedly earmarked for a Northern Ireland politician".
Meanwhile, the Finance Committee of the Stormont Assembly, which is considering the claims, has said it wants to begin hearing evidence next week.
It is to invite Mr Wallace along with representatives of NAMA and the Belfast law firm involved to answer questions.
However, it is understood that Mr Wallace sees no purpose in acceding to that request either.
Finance Committee Chairman Daithí McKay said it would be asking the questions the public are asking.
'Enormous concern' about NAMA - Martin
Fianna Fáil leader Micheal Martin said there had been "enormous concern" at the sale of NAMA's loan book in Northern Ireland, raised by Deputy Wallace last week.
Mr Martin said Finance Minister Michael Noonan had asked the agency about selling the portfolio in a six month period.
He said the entire property was in one bundle, what we know now is that £7m ended up an Isle of Man account.
We know that another large US firm, Pimco, withdrew citing concerns about an unsolicitated approach.
He said NAMA has confirmed this. Mr Martin said he was not naming any names, but the law firm said the former partner had diverted funds without their knowledge.
He said this raised concerns, given the gravity of what has been alleged, that a commission of investigation was now required.
Mr Martin asked if the Government had made that decision.
Minister Richard Bruton, taking leader's questions on behalf of the Government, said a member of the Controller and Auditor General was embedded in NAMA.
He said PAC would have an opportunity to question NAMA represenatives about how the conduct their affairs.
Separately, the Law Society for Northern Ireland has confirmed it is conducting an inquiry into the circumstances which led to the resignation of Ian Coulter from the Tughans law firm in Belfast.
In a statement released last week, Tughans said: “a former partner diverted to an account of which he was the sole beneficiary of professional fees due to the firm, without the knowledge of the partners.
"We have since retrieved the money and he has left the practice. Tughans reported the circumstances of the departure of the former partner to the Law Society."
The Law Society says it is satisfied any funds in question are secure while the investigation is ongoing.
It says Mr Coulter did not renew his practising certificate in 2015 and is not therefore a practising solicitor in Northern Ireland.
