Micheál Martin has said he "gets on well" with Leo Varadkar - but he dodged a question surrounding the Garda investigation into the Fine Gael leader.
Social Democrats co-leader Roisin Shortall has suggested there would be a problem if there is an investigation ongoing when Mr Varadkar is due to be Taoiseach again in December.
Last year, gardaí confirmed an investigation was underway into the circumstances surrounding the disclosure of a confidential Government document to a friend of the Tánaiste over two years ago.
When asked by RTE's Rachael English on Morning Ireland whether Varadkar taking office again would be appropriate, the Taoiseach said: "We need to be careful of pre-judging on outcomes. We would like that issue to be resolved once and for all. My view is that... I'm not going to get involved or comment on the process itself.
"I'm working well with the Tánaiste and Eamon Ryan."
When asked again, he replied: "I'm not going to comment around that.
"We have to observe due process and not attempt to pre-judge situations. I don't think that's fair either.."
NPHET will meet on Thursday afternoon to analyse the latest data surrounding Covid-19 and make their recommendations to Government.
It is expected that the group, led by Chief Medical Officer Dr Tony Holohan, will give the green light to the Government to re-open the country further.
This will likely include the end of the 8pm curfew on hospitality, the return of crowds to indoor and outdoor events (including sports) and a future plan for the rest of the spring and early summer.
The Taoiseach gave further clarity during the Morning Ireland interview.
