Meghan Gallacher has quit as deputy leader of the Scottish Conservatives.
It comes amid concerns the party's leadership contest could be at risk following reports about the alleged conduct of Douglas Ross in relation to the general election.
Ms Gallacher, who is one of six MSPs in the race to replace Mr Ross as leader, said she is unable to continue as deputy leader due to the potential "reputation" risk to the party.
She said on X she was "deeply troubled" by reports in the Telegraph that Mr Ross allegedly asked Moray West, Nairn and Strathspey Tory candidate Kathleen Robertson if he could replace her in July 2023 - a claim he has denied.
Ms Gallacher's resignation comes after four other candidates - Murdo Fraser, Brian Whittle, Liam Kerr and Jamie Greene - wrote to the party to demand "serious questions" be answered over the allegations.
The leadership contenders said they needed answers to allow the contest to "proceed".
In her letter to Mr Ross, Ms Gallacher said: "I was completely unaware of discussions surrounding a candidate that took place in July 2023. Following the story being published, there is a potential risk to the reputation of our party and the leadership contest moving forward."
She also said it was "regrettable" that the leadership team had not contacted her in her position as deputy since the allegations came to light.
Ms Gallacher also cited her leadership candidacy as a reason for her resignation, stating there is a "conflict of interest" in remaining as deputy.
She told Mr Ross: "I will not be able to assist you as I have been excluded from doing broadcast and media on behalf of the party, as part of my candidacy.
"It is with great sadness that I tender my resignation as deputy leader."
Mr Ross said in response: "It is with regret that I accept your resignation as deputy leader.
"It has been a pleasure to work with you over the last two years to take the Scottish Conservative Party forward and challenge the SNP government."
He said he accepted her reasoning of "conflict of interest" concerns, and added: "I have committed to remaining neutral in this contest."
Mr Ross is alleged in the Telegraph to have told Ms Robertson that his "heart was in Westminster, not Holyrood", but it is claimed she refused the request to stand aside despite being promised selection as a Holyrood candidate in 2026.
The newspaper also reported Mr Ross told her he would prefer leadership candidate Russell Findlay to replace him.
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A letter from Mr Fraser, Mr Whittle, Mr Kerr and Mr Greene said: "As candidates for the leadership of the Scottish Conservative and Unionist Party, we are deeply concerned by the disturbing claims reported today about the conduct of Douglas Ross in relation to his seeking candidacy for a number of seats in the recent general election.
"The reports also reference his plans and preferences for a replacement leader to take over the party upon his departure which are relevant to the transparency and fairness of the current leadership contest we are participating in.
"These allegations raise serious questions for the party which, in our opinion, require to be answered before current leadership election proceeds further."
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Tap hereMr Ross previously ruled out standing at Westminster to focus on his Holyrood priorities as leader and Highlands and Islands MSP.
But he U-turned during the 2024 election, announcing he would seek election in the Aberdeenshire North and Moray East seat, facing further criticism after ex-MP David Duguid said he was "deselected" the night before the announcement due to ill health.
Mr Ross then announced he would step aside as party leader.
He lost the seat to the SNP and now faces calls from the nationalists to resign from Holyrood.
Mr Ross told the Telegraph he sought the meeting with Ms Robertson at the request of local members to check she was "still committed to standing for the seat".
He said: "She confirmed that she was and I then campaigned with her in the hope that she would win the new constituency."
On the Telegraph claim that Mr Ross told Ms Robertson he wanted Mr Findlay to replace him as Holyrood leader, he told the newspaper: "Throughout the leadership election I have said absolutely nothing about the candidates or the contest, other than I will remain as leader until my successor is appointed. My decision to remain neutral throughout the contest will not change."
A Scottish Conservative spokesperson said: "This relates to a personal and private conversation between Douglas Ross and Kathleen Robertson and is not a matter for the party.
"Some months later, Kathleen Robertson separately informed the chairman and the party director about this meeting and said she wished this matter to remain confidential and required them to do nothing further."
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