Prime Minister John Key says Labour MP Chris Carter's request to be on leave from Parliament feels like an excuse.
Mr Carter was suspended from Labour's caucus on Thursday for circulating an anonymous letter detailing discontent with party leader Phil Goff and predicting a leadership challenge.
On Monday the Labour Party issued a statement, saying that the Te Atatu MP - who is taking about two months' leave from Parliament - is unwell and is getting appropriate help.
Mr Key says Mr Carter is going to have to tell the New Zealand public that he genuinely believes he's sick, because he was asked that question last week and said no.
The Prime Minister says that the views Mr Carter expressed in the letter are broadly held in Labour's caucus and that he is not a lone voice.
"Might be a hamfisted way of going about it," Mr Key says, "but I think there is widespread concern in that caucus." Mr Key adds, however, that he does not have any evidence.
Reopening of nominations likely
The Labour Party will make no immediate decision on whether to kick Mr Carter out of the party, but it is set to reopen nominations for his seat.
Labour's New Zealand Council was to have considered the MP's future at a meeting this Saturday but because of his taking leave, party president Andrew Little says, it will not now do so this weekend.
Mr Little says, however, that the council is likely to decide to reopen nominations for Te Atatu, which Mr Carter has held since 1993.