Simon Bridges isn't ruling out keeping the leaker of his expenses, should they be an MP, in his caucus.
The details of the National Party leader's spending were released days ahead of schedule after someone sent them to Newshub.
An investigation launched by the Speaker was called off after it was determined the leaker was someone inside the National Party itself.
Asked if it was an MP, would he sack them, Mr Bridges told Newshub Nation on Saturday he would "have to see what the circumstances are" before making a call.
"It will be a mixture, I think, of being clear and strong, because it's not good enough if it was one of us, and we just don't know that yet," he told interviewer Lisa Owen.
"Let's go through the process and see. But we also know there are some other issues at play here, potentially in terms of wellbeing and so on, so we'll just have to, look, actually exercise some clear, effective leadership on that."
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A text message believed to be from the leaker was sent to Newshub political editor Tova O'Brien, Speaker Trevor Mallard and Mr Bridges in the days following the leak, begging for the Speaker's investigation to be called off, citing mental health issues.
National has since launched its own inquiry.
"We've got a process that's weaning its way along, trucking along, and we'll see where we get to. I ultimately don't know who it is. What I'd say to you, Lisa - if - and it is a big if - if it is a National Party MP or a staffer, I will be incredibly disappointed. But I'll tell you what - all of my other colleagues, my members of Parliament will also be very disappointed about that."
Despite hiring two agencies to assist the party with the search, Mr Bridges insists it's not "worth getting too hung-up on".
"We've got a process going on. I don't think about it. I've got Gerry Brownlee and Paula Bennett doing it."
Mr Bridges in August said police had worked out the leaker's identity, and were making sure they were getting the help they needed.
"At no time did police tell me that the [internal] investigation should not proceed," he said at the time.