There is a warning that taking legal action against Eygpt over its treatment of Ibrahim Halawa could hurt his chances of being released.
The 21-year-old Dubliner has been held in jail for almost four years with his mass trial postponed 26 times.
It has emerged officials in the Department of Foreign Affairs are concerned legal action by the Halawa family would be seen by Cairo as a hostile move.
However, Ibrahim's sister Somaia does not believe Egypt's promise to deport him after the trial concludes.
She said: "First of all, we know 100% that Egypt hasn't kept any promises.
"First they said the trial is coming to an end, that was two years ago, and now we're coming up to four years and the trial is still dragging on."