Taoiseach Brian Cowen says there is no indication when the by-election in Donegal will take place.
It comes despite claims by Green Party Senator Dan Boyle that the contest could be held in the Autumn.
Over the weekend, Senator Boyle said it may coincide with the Children's Rights Referendum.
The Coalition is being criticised for the delay in calling the three outstanding by-elections, amid accusations from the Opposition that the Government is running scared because it knows it is unlikely to win them.