An MP who defected from the SNP to the Tories over bullying claims was having a “tantrum”, the SNP president says.
Mike Russell rejected Lisa Cameron’s claims that a “toxic” culture in the party had affected her mental health.
Dr Cameron was facing an SNP selection contest to remain as candidate for East Kilbride, Strathaven and Lesmahagow at the next general election.
Mr Russell said her constituency party lost faith in and her “unsubstantiated” claims should be examined.
Prime Minister Rishi Sunak welcomed Dr Cameron – a former NHS clinical psychologist – after she announced she had joined the Conservatives on Thursday.
SNP leader Humza Yousaf called on her to step down to allow a by-election.
In her departure statement, Dr Cameron rowed back on her support for Scottish independence and described it as “divisive”.
Mr Russell told BBC Radio’s Good Morning Scotland programme that Dr Cameron’s relationship with the SNP had “become more and more fraught over the years”.
He said: “Lisa’s decision is her decision, but I regard it as absolutely bizarre and I think it does call into question all sort of things.”
Mr Russell said the SNP needed to focus on the big issues in Scotland and “not what seems to be a rather odd tantrum from somebody who was going to lose their seat and lose their nomination.”
He added: “That was absolutely clear – the constituency party had lost faith in her, and I think that kind of ego-driven politics is deeply unattractive.”
She said a “toxic and bullying SNP Westminster group” resulted in her requiring counselling for a year and caused “significant deterioration” in her health including the need for GP-prescribed antidepressants.
However, the SNP president challenged this.
Mr Russell told the BBC: “I think Lisa’s claims are unsubstantiated and what we need to focus on is reality.
“I have the greatest sympathy for anybody in those circumstances, but their claim for how they arose, when they make that claim publicly, has to be regrettably examined.”
He said the East Kilbride, Strathaven and Lesmahagow MP should stand down to allow for a by-election in the constituency.
‘Dismissing concerns’
Meanwhile, Mr Russell said Western Isles MP Angus MacNeil should also stand down for a by-election to be held.
Mr Russell said: “He has changed his position and that requires a new mandate, just as the people in East Kilbride are entitled to ask to exercise their mandate.”
At the time, she did not rule out standing down and triggering a by-election if she did not win the SNP nomination.
Scottish Conservatives chairman Craig Hoy told the BBC that Mr Russell was “dismissing the concerns raised by Lisa Cameron in the most high-handed of ways”.
He added: “She is a brave and committed constituency MP and I think she’s been right in saying we need to show more empathy in politics and focus on less division.”
He said that there was no need for a by-election as “other parties have welcomed new MPs without one”.
Mr Hoy added: “The party that loses an MP in a defection always demands a by-election, but it’s not always a necessary part of our constitution.
“She will continue to represent her constituents in the same way she has done in the last four years.”