Former Labour MP Judith Tizard says party leader Phil Goff must ask himself whether he can win the next election.
Ms Tizard announced on Sunday she will not return to Parliament to take Darren Hughes' list seat.
But she accuses former party president Andrew Little of bullying her by publicly suggesting she and four others on the party list should decline the chance to replace Mr Hughes.
Ms Tizard will not be drawn to comment directly on Mr Goff's performance, but says he should analyse his chances of success at the election and stand aside if he can't win.
Ms Tizard, 55, was an MP for 18 years until she was defeated in Auckland Central in 2008.
She says she wonders how Mr Goff would deal with New Zealand First leader Winston Peters and the Maori Party co-leader Tariana Turia if he cannot deal with her.
Mr Little says her views are not widely supported in the party. He accepts he should have spoken to her before talking publicly, but says in no way did he bully her.
Mr Goff says he can win the election. He told Morning Report that he has been elected unanimously as leader twice now by the party which has confidence in him.
He accuses the media of being obsessed with who should lead the party into the general election on 26 November.