Public Accounts Committee (PAC) chairman Seán Fleming has said Nama was unable to demonstrate that it got "value for money for the Irish State" following the sale of the largest property portfolio in the history of the State.
Mr Fleming issued the warning following the publication of the PAC report into the controversial sale.
"The committee is firmly of the view that the sale of Project Eagle was not a well-designed sales process," Mr Fleming said.
The Fianna Fáil TD also raised serious concerns about a decision by Nama to destroy contemporaneous notes of board meetings relating to the sale of the loan book.
The PAC also criticised Finance Minister Michael Noonan for meeting senior representatives from Cerberus, the winning bidder of the property portfolio, the day before the bidding process ended.
In its final report on the Project Eagle loan book sale, the PAC said it considered that it was "procedurally inappropriate" for Mr Noonan to meet the US investment firm prior to the process.
Mr Fleming said the meeting could have given the impression that Cerberus was "benefiting from preferential treatment".
In a statement, Mr Noonan said he "absolutely" rebuffs that he or his officials acted inappropriately in their dealings with Cerberus.
At a press conference, Fine Gael TD and PAC member Peter Burke said the minister had been "denied natural justice" because he was not given a chance to respond to the accusation before the Committee's report was published.
Mr Fleming, however, said Mr Noonan was not asked about the meeting when he appeared before the PAC because members did not know he had met Cerberus at that point.
The committee also criticised Nama chairman Frank Daly and chief executive Brendan McDonagh for not informing the agency's board that they met with Cerberus on the day before the bidding process ended.
The PAC recommended that the Government establish a commission of investigation to examine the sale of Nama's Northern Ireland loan book.
The report will be debated in the Dáil in the coming weeks.