Alex Salmond believes Nicola Sturgeon and her circle have been “stitching him up”, according to a friend.
SNP MSP Alex Neil said anyone proven to be involved in a conspiracy against the former first minister would be “getting their jotters” (sacked).
Mr Neil, who represents the Airdrie and Shotts constituency, is not seeking re-election in May.
He is an ally of Mr Salmond and has previously said he would welcome the former first minister returning to Holyrood.
Mr Neil told BBC Radio 4’s Today programme on Thursday: “He believes that there was a conspiracy to get him.
“Initially he thought it was an attempt to keep him out of public life and not allow him back into the Scottish Parliament after he lost his Westminster seat.
“But I think since then this has grown and he believes a number of people have been involved in conspiring against him and stitching him up.”
Asked if Mr Salmond believes Ms Sturgeon and her circle were involved in a conspiracy to “do him down”, Mr Neil replied: “Basically, I think he does, yes.
“I think Alex believes after he lost his Westminster seat there was a possibility of a by-election in Scotland in his neck of the woods and he believes some people were frightened of him coming back in, which he says he had no intention of doing anyway.”
Mr Neil’s statement comes amid a row over an inquiry into the handling of harassment complaints against Mr Salmond.
The MSP also told the Today programme: “I think there’s a real problem now because this is starting to dominate the airwaves at a time when we’re still dealing with the pandemic and also, in four weeks’ time, we go into the initial start of the election campaign.
“I think the SNP leadership has got to try and put a lid on this.
“If it was proven there was a conspiracy – everybody involved in the conspiracy, I think, would be getting their jotters.”
On Wednesday, Ms Sturgeon addressed claims from Mr Salmond when she was asked about them at her coronavirus briefing.
She repeated her assertion that there is not “a shred of evidence” to support her former mentor’s claim of a “malicious and concerted” attempt to remove him from public life.
She also strongly denied the Crown Office’s intervention earlier in the week – which led to a Holyrood committee partially redacting evidence it had received from Mr Salmond – was politically motivated.
The First Minister said: “Any suggestion at all that these decisions are in any way politically influenced are downright wrong.
“I would suggest that they go further than that; that they actually start to buy into what is a false and quite dangerous conspiracy theory that has no basis in fact.”
Later on Thursday, an SNP spokeswoman said: “It is up to Mr Salmond to provide evidence for his baseless claims of a conspiracy.
“Several of the women complainers have already said how utterly absurd it is to suggest they would have lied under oath.”