There is no future for NI21, the party's former deputy leader has insisted.
And John McCallister said his ex-political partner Basil McCrea, who remains leader, has been left "clinging to the wreckage".
His trenchant attack came just a few days after Mr McCallister resigned from the party in the aftermath of a series of allegations against Mr McCrea, which he strongly denies.
Mr McCallister, who is to remain as an independent unionist in the Assembly, also revealed the key lesson he had learned from the experience was "don't start a political party with Basil McCrea".
The South Down MLA – who quit the Ulster Unionists alongside Mr McCrea last year – also told the BBC Sunday Politics programme he intended to fight the seat at the next Assembly election in 2016.
Asked if he thought NI21 had a future, he said it wasn't for him to decide.
But he then said: "I don't think it does have a future."
Northern Ireland's newest political party has been on the brink of collapse since a public fall-out between Mr McCallister and Mr McCrea after the former instigated an external investigation into allegations of inappropriate sexual activity against his former colleague.
Mr McCrea has denied the allegations.
Speaking about his reasons for standing down, Mr McCallister said his position as deputy leader, chief whip and member of NI21 had become untenable after the investigation by mediation firm Carecall was halted by the party.
The allegations have now been referred to the Assembly's commissioner for standards.
Mr McCrea has insisted he has a "story to tell" but is intending to take legal action.