Conservative leadership candidate Jeremy Hunt has said he would never allow the break up of the United Kingdom if he becomes prime minister.
Speaking at an event in Aberdeenshire, Boris Johnson's rival said he would support the union with "every drop of blood in my veins".
His comments come after Scotland's first minister said Mr Johnson would be "disastrous" for the Scottish Tories.
Boris Johnson is the front-runner to replace Theresa May in Number 10.
Speaking in Peterhead, Jeremy Hunt told local Conservatives that he would fight to preserve the United Kingdom.
It follows a poll of 1,024 Scottish voters for the Sunday Times which found that more than half would vote to leave the UK if Boris Johnson were to become prime minister.
Nicola Sturgeon has already earmarked the second half of 2020 for when a second Scottish independence referendum could be held.
Mr Hunt told Conservatives: "I'm in Scotland today because I'm the prime minister that Nicola Sturgeon does not want because I passionately support the union with every drop of blood in my veins.
"I will never allow the union to be broken up as prime minister."
He added: "I would never pay any price if it meant that Scotland would become independent."
He was referring to another recent poll that suggested a majority of Conservative Party members wanted Brexit even if it meant Scotland gaining independence.
Mr Hunt replied: "I don't actually believe that polling.
"Conservative Party members I know are absolutely passionate about our precious union."
The foreign secretary also said that the public did not want a debate on his Tory leadership rival's private life.
Boris Johnson has .
"It's up to him what he says, but I don't think the public, and I don't think Conservative Party members, want a big debate about people's personal lives," Mr Hunt said.
He added that they wanted a "proper debate" about how "we're going to get out of the "Brexit constitutional crisis".
In an interview with Sophy Ridge on Sky News, Ms Sturgeon was asked her views on the impact choosing Boris Johnson as prime minister would have on the Conservatives in Scotland.
She said: "I think he would be devastating, disastrous for the Conservatives UK-wide but particularly in Scotland.
"He is seen in Scotland I think as one of the principle politicians who are responsible for the mess that we are in over Brexit, the guy who misled people in the EU referendum campaign and the guy who now says he is prepared to take the UK out of the EU without a deal, for most people in Scotland that is a horrifying prospect."
Ms Sturgeon also said that Mr Johnson had made "overtly racist" comments when he ".
Speaking on the BBC's , Conservative MP for Aberdeen South, Ross Thomson responded to Ms Sturgeon's comments by saying: "As usual, Nicola Sturgeon is using any opportunity to whip up support for her separatist agenda.
"The truth is that Boris Johnson is absolutely committed to not just protecting, but to strengthening our union if he becomes PM."
It comes as the said Mr John should "just give an explanation" about the row recorded at his home by a neighbour earlier this week.
The MP said reports of the row between Mr Johnson and his partner should not be a "distraction" from policy discussion in the leadership race.