The Minister for Transport will insist the new Aer Rianta chief executive, Ms Margaret Sweeney, is appointed on a temporary basis, ahead of the break-up of the airport authority early next year.
Mr Brennan has told the Aer Rianta board he will only approve the appointment of Ms Sweeney, announced yesterday, if she is given the title acting chief executive, underlining the transitory nature of her position.
Should the Minister's plan to dissolve Aer Rianta into three autonomous governing bodies for Dublin, Cork and Shannon airports, proceed on schedule Ms Sweeney - who succeeds Mr John Burke from January - could see her position defunct by spring.
There is no question of Ms Sweeney, who is currently Aer Rianta deputy chief executive, receiving a settlement when the organisation ceases to exist, said a spokesman for the Minister.
It is believed Mr Brennan had hoped Mr Burke would continue to serve on an interim basis, pending the dissolution of Aer Rianta.
Aer Rianta said the details of Ms Sweeney's appointment - including its length - are still being discussed.
"The fine print of the contract is being worked on," said a spokesman. From Kilcar, Co Donegal, Ms Sweeney joined Aer Rianta in 1997, having previously served as a director of KPMG.
She represents Aer Lingus on the boards of the three overseas airports in which it has a shareholding: Birmingham, Düsseldorf and Hamburg.
Mr Burke will continue to serve in the capacity as adviser to Aer Rianta.
The position of chief executive currently commands a €315,000 remuneration package.
The Bill providing for the establishment of the new airport bodies is expected to be published before the end of the month.