Candidates must secure the nominations of three MPs and three MSPs in order to get onto the leadership ballot, but The Herald understands conversations have taken place where parliamentarians have been urged to block Ms Lennon.
Sources told The Herald that Mr Marra has the “party machine” behind him, while Joe Fagan, the third candidate in the race, is favoured by Dame Jackie Baillie – the current interim leader.
Mr Marra’s team have rejected the claims and said “negative anonymous quotes” were damaging to the leadership contest and the party.
Brian Leishman, Alloa and Grangemouth MP, has endorsed Ms Lennon for the leadership, alongside Falkirk’s Euan Stainbank.
But so far, no MSPs are yet to endorse her while Marra has the public backing of at least five MSPs.
Mr Leishman told The Herald: “MPs and MSPs being placed under pressure to block any candidate would be an affront to the values of the Scottish Labour Party, and to wider democracy.
“Our Scottish Labour members deserve better than that. They deserve, and must have, the opportunity to engage in a robust debate of ideas and beliefs and then make the decision on the future direction of our party.
“To be a truly democratic and accountable organisation, then the membership should have the choice of different candidates.”
He added: “It’s important that the Scottish Labour membership are provided with a genuine contest with candidates that are representative of different views.
“Things absolutely must change, we cannot carry on with the failed policies and politics that have seen us reduced to our lowest total of MSPs ever.
A senior Labour source told The Herald: “It is no secret to anyone that Michael has been plotting for the leadership for a significant period of time, only he expected there would be a coronation when Anas resigned.”
Michael Marra (Image: Scottish Parliament)
Mr Marra has the backing of MSPs Neil Bibby, Jenny Young, Daniel Johnson, Pauline McNeill and Claire Baker.
“If there are candidates that are phoning around then it’s clear they have learned absolutely nothing.
“If they were confident they could beat Monica, there would be no need for the briefings. It comes down to giving members a choice.
“Marra has been manoeuvring for leadership for quite some time now, while Monica from the backbenches brought two popular pieces of legislation through – members are eager for a change.”
“There is a danger for Labour members that this contest will be decided before the ballot even opens on Monday,” the source added.
“That is the last thing that members want.”
Concerns around Ms Lennon’s leadership centre on her pro-trans stance and comments she made on Scottish independence when running against Mr Sarwar in 2021.She said it would be “foolish” to ignore the wishes of voters if they expressed a wish for a second referendum.
Ms Lennon was defeated in 2021 with 42.44% of the vote but still remains a favoured candidate among grassroots activists.
Another source said: “I’ve heard firsthand of conversations between Monica and MSPs who have said things to her and then turned around and done the opposite, by backing another candidate.
“Obviously it’s a leadership contest and politics is a contact sport but I think the real point is that members don’t want a coronation and they don’t want an artificial competition.”
“Monica is still very popular with the wider membership and if it becomes clear that MSPs and MPs are doing this, then I think the membership will take a really dim view of this.”
“On the face of it, everyone is saying that we need to have a proper debate and yet they’re shutting down one of the clearest avenues of debate which would be have somebody ostensibly from the left versus someone from the centre-right and that doesn’t sound like somebody who wants a debate.
“This is no surprise to any of us but we’ve had six successive Holyrood election defeats and this just smacks of let’s just go around the exact same cycle of madness.
“We’re not going to find the change we need by stitching up another leadership election.”
Responding to the claims, Pauline McNeill and Tracy Gilbert, co-chairs of Mr Marra’s campaign said: “We welcome all candidates to the contest and would encourage all campaigns to conduct themselves in the positive and comradely fashion that party members expect.
“It is up to individual parliamentarians to nominate who they believe offers the best leadership for the party.
“Michael has spent the last week listening to colleagues, and everyone has been clear that the last thing the party needs is for a culture of negative anonymous quotes and briefings to continue, party members deserve better than this.
“We would urge all campaigns to dissociate themselves from that behaviour.”
Ms Lennon, on an Instagram video, alluded to issues, stating she did not have the “machine” behind her and insisting she was not “preparing” for the leadership before Mr Sarwar resigned.
“I just want this to be a genuine, open debate where our grassroots supporters feel respected and not just used at elections to be the people that go out on the door come rain or shine,” she said.