Sir Ed Davey claimed the Prime Minister had not campaigned north of the border because he was a hindrance to the campaign.
Speaking ahead of a visit to Scotland next week, the Kingston MP also claimed the Conservatives were struggling because of the leadership of Scottish Tory leader Douglas Ross.
He said: “We think the mood swing isn’t just against the SNP, it’s against the Conservatives.
"It isn’t just Boris Johnson’s scandals, which I don’t think will be welcomed by former Conservative voters, but also Douglas Ross has gone down very badly.
“I think his overall tone has put Conservatives off and he’s not a patch on Ruth Davidson.
"He’s Boris Johnson’s person. He was a minister in his government and he continues to vote with Boris Johnson.
"Boris Johnson is mired in scandal and he’s not the sort of person you want on your campaign trail.
“I personally think the multiple witnesses to his alleged comments about bodies piling high is just so callous and so awful.
“Why would anyone want somebody like that to come to their aid on a campaign?
“He has some unpleasant views, he’s played the campaign in a very dark way and it just hadn’t gone well.”
Sir Ed’s comments come despite Mr Ross previously resigning from a role in the UK Government over the saga involving the Prime Minister’s former chief aide Dominic Cummings.
It comes amid a growing backlash against Mr Johnson over reports he said he would rather see "bodies pile high" than take the country into a third Covid lockdown.
Despite the Prime Minister denying he made the remarks, new polling by YouGov found 50 per cent of people across the UK believe he did say the comments, compared to 65 per cent in Scotland.
Mr Johnson is also facing questions after refusing to answer who initially paid for the Downing Street renovation as the Electoral Commission launched an investigation into Tory Party donations towards the works.
The commission said there were "reasonable grounds to suspect that an offence or offences may have occurred", but insisted its inquiry into the affair was related to the Conservative Party and not the Prime Minister personally.
This week it also emerged the Prime Minister’s mobile number had been posted online and was freely accessible for more then a decade.
The SNP’s Westminster leader Ian Blackford has urged the UK Government's newly appointed independent advisor on ministers' interests to urgently investigate the Prime Minister's correspondence on Covid contracts.
Mr Blackford has written a letter to Lord Geidt asking for the publishing of such correspondence to be an urgent priority given the mounting allegations of breaches to the ministerial code of conduct involving Mr Johnson.
"It is now a full nine days since Boris Johnson promised to publish all of his Covid contract correspondence ‘immediately’ – and still nothing," he said.
"The allegations of Tory sleaze continue to pile up and yet not a single piece of this correspondence has been released, leading to concerns that evidence might ‘go missing’.”
SNP Westminster depute leader Kirsten Oswald separately claimed Scots could “see right through” Mr Johnson’s “dishonesty”.
The Scottish Tories have been approached for comment.