The Fianna Fáil leader Micheál Martin says a decision to add Sean Haughey to the election ticket in Dublin Bay North was made independently.
Councillor Deirdre Heney last week hit out at the development, after she won a place at a selection convention during the summer.
She claimed it was proof of a culture of the "old boys brigade" in the party, and said she was "very disappointed" by what Mr Martin had allowed to happen to her.
However, Deputy Martin insists the decision was made by the Fianna Fáil's constituencies committee, and he says he understands that competition can cause problems.
He said: "What we're witnessing in the party is increased competitiveness, people looking to become nominated, more than just one.
"Compared to 2011 it's a sea-change in terms of the internal competition, and that creates tensions, I acknowledge that.
"In some instances it creates anger, it creates disappointment because people would be looking for a configuration or selection that would best suit their own position."