Minister for Justice Alan Shatter has said he will bring to Cabinet the request for an extension of time for the Smithwick Tribunal.
Judge Peter Smithwick is investigating claims of garda collusion with the IRA in the murder of the two most senior RUC officers to die in the Troubles.
Chief Supt Harry Breen and Supt Bob Buchanan died in an ambush minutes after leaving a meeting in Dundalk Garda Station in March 1989.
In his letter to the Oireachtas seeking an extension of time, Judge Smithwick said that "fundamental witness" former Det Sgt Owen Corrigan was ill and would not be in a position to return to give evidence to the Tribunal until March or April of next year.
He is one of three former gardaí being investigated by the Tribunal.
Judge Smithwick said he had also received intelligence from the British security forces that is of "considerable relevance" to the Tribunal and this needed to be investigated.
He said he is seeking an extension to the end of July next year.
A spokesperson for Mr Shatter said he would be bringing the matter to Cabinet for consideration "in due course".
The granting of an extension is ultimately a matter for the Oireachtas to decide, but Mr Shatter’s views are likely to carry considerable influence among Government TDs and senators.