Businessman Frank Cushnahan was aware of US investment firm Pimco's interest in purchasing Nama's northern loan portfolio at least a month before he resigned as an adviser to the agency.
Mr Cushnahan's knowledge of Pimco's interest in the Project Eagle loans was confirmed by documents seen by the Irish Independent.
Nama had previously stated that the former banker, who advised the agency in the North for three years, did not have access to confidential information relating to the sale, including the identity of bidders.
However, the minutes of a meeting of Nama's Northern Ireland Advisory Committee (NIAC) on October 7, 2013, show Mr Cushnahan and others present were informed by Nama chairman Frank Daly that Pimco had made "an unsolicited approach" for the portfolio.
Just over four weeks later, Mr Cushnahan quit his role with Nama, citing family priorities.
However, unknown to the agency, he went on to act as an advisor to Pimco.
Nama was informed by Pimco in March 2014 that Mr Cushnahan stood to earn Stg£5m in fees if Pimco was successful in buying the portfolio.
Pimco voluntarily withdrew from the bidding after Nama raised concerns about the proposed fees.
It is not known what specific services Mr Cushnahan provided to Pimco.
A statement issued by Mr Cushnahan's solicitor last month said he firmly denied any wrongdoing and would fully co-operate with any police investigation.
The Project Eagle portfolio, comprising loans given to 55 debtors from Northern Ireland and secured on around 900 properties, was subsequently sold to US vulture fund Cerberus for €1.6bn in April 2014.
The sale has been dogged by controversy following allegations by Independent TD Mick Wallace that Stg£7m in an Isle of Man account was destined for a Northern Ireland politician or party.
Cerberus has denied making or planning any inappropriate payments, while the solicitor who controlled the account, Ian Coulter, has also denied any impropriety.
The deal is now being investigated by the UK's National Crime Agency and parliamentary committees on both sides of the border. The US Department of Justice has also reportedly issued a subpoena to Cerberus seeking information.
The minutes of the October 2013 NIAC meeting were supplied by Nama to the Northern Assembly's committee on finance and personnel.
Although the same record was previously released under the Freedom of Information Act, a section referring to Pimco had been completely redacted.
It stated Mr Daly informed the meeting of Pimco's unsolicited approach and the fact that preliminary discussions had taken place. The minutes said the matter had been discussed by the Finance Minister Michael Noonan and his northern counterpart Simon Hamilton. It said Mr Noonan had informed Mr Hamilton it was "a commercial matter for Nama".
Mr Daly told the meeting the matter was "extremely politically sensitive and that absolute confidentiality was required".
Last night, Nama said it stood over previous statements in which it said Mr Cushnahan was not given access to sensitive information, including the identity of bidders.
It said the approach detailed in the minutes "was not a bid" and that Nama had decided against entering into an exclusive sales process, as had been sought by Pimco.