Momentum’s Jon Lansman is tipped to stand as a grassroots candidate for Labour general secretary, the Guardian understands.

Iain McNicol, Labour’s longstanding general secretary, stepped down at the end of last week.

He is expected to be replaced with a leftwinger, with the Unite officer Jennie Formby previously tipped as the leading candidate to replace him.

Many in the party strongly believe McNicol’s replacement should be a woman, given most key Labour positions are held by men.

Others who have been tipped for the position are the GMB union’s Lisa Johnson and Unite’s political director, Anneliese Midgley.

However, sources at Momentum, the leftwing group that has supported Jeremy Corbyn’s leadership, said there was dissatisfaction that the role should be chosen behind closed doors by Labour’s national executive committee (NEC), which in practice would mean a deal struck between major trade unions for their preferred candidate.

McNicol, who had become a focus for attacks by Corbyn’s supporters during the previous Labour leadership contest, is understood to still be in negotiations about his departure.

He addressed a private meeting of the parliamentary Labour party on Monday night in the House of Commons, receiving cheers and extended round of enthusiastic applause from MPs and peers as he entered the room.

Earlier on Monday, the NEC agreed that the new general secretary would be appointed at the next meeting of the governing body on 20 March.

Senior Momentum members have said they are unhappy with the process and may urge the leadership to change course on the appointments protocol to allow for an election of the general secretary, though that would be likely to require a rule change at the party’s next annual conference.

A senior Momentum source said: “Jon has an unparalleled track record in fighting for party democracy over the past 30 years. Jeremy’s style of politics is not that of backroom deals, but of open and transparent discussion, which is exactly what Jon would represent as a candidate.

“Jon has proven his popularity with the membership with his recent NEC election result and I’m sure he would pick up significant support if he did throw his name in the ring for the general secretary’s job.”

Johnson, the GMB’s political officer and a potential compromise candidate, has told friends she is happy to remain in her current role, though she could yet be persuaded to stand.

A Labour source said the shadow chancellor, John McDonnell, was keen to promote Formby as a rival to Karie Murphy, Corbyn’s chief of staff.

However, an ally of the shadow chancellor insisted: “This is nonsense. John and Karie are of the same mind on bringing in Jennie. There is not a fag paper between them on these decisions.”

