The Foreign Secretary made the remarks when questioned in the Commons about how the Assad regime could be punished for using chemical weapons without allowing a “virulent Islamist regime” to replace him.
Mr Johnson said he agreed with the wisdom of the remark, which came from Julian Lewis, Conservative chairman of the defence select committee.
He said: "The essential thing will be to have a political process that preserves the institutions of the Syrian state while decapitating the monster.”
The Foreign Secretary has previously said there will be “no impunity” for those responsible for the chemical weapons attack earlier this month, which killed at least 80 people.
Boris Johnson described President Assad as a 'monster'
Hundreds of others suffered symptoms consistent with reaction to a nerve agent after what the opposition and Western powers described as a Syrian government air strike on the rebel-held town of Khan Sheikhoun in north-western Syria.
The Syrian military denied using any chemical agents, while its ally Russia said an air strike hit a rebel depot full of chemical munitions.
According to Mr Johnson, Britain may also be likely to support the United States in the event of ay further missile strikes on Syria, saying it would be “very difficult” for the UK to say no to a request for support from the US.
Horrific images depict sickening chemical gas attack in Syria Tue, April 4, 2017
At least 58 people, including nine children, were killed in an air raid that released "toxic gas" on the rebel-held Syrian town of Khan Sheikhoun
EPA 1 of 13
A child receiving treatment at a field hospital after an alleged chemical attack in Idlib, northen Syria
Earlier this month, the US fired 59 Tomahawk missiles at a Syrian airbase suspected of launching the chemical attack.
The Foreign Secretary confirmed the UK was not asked for any specific support ahead of that strike, which was the first direct military action taken against President Assad by the US.
Get Quotes on Home Insurance
Russian Foreign Minister Sergei Lavrov said a chemical-weapons attack in Syria that provoked US missile strikes on the Middle Eastern country may have been orchestrated.
Speaking at a news conference with his Iranian and Syrian counterparts, Mr Lavrov said: “There’s growing evidence that this was staged.” He went on to claim there were “many inconsistencies” in the justification of American airstrikes.
He added that Russia, Iran and Syria want an independent investigation into the events, claiming those opposed to the call “don’t have a clear conscience”.
Mr Johnson has encouraged Russia to end its "blind support" for the Assad regime.
The call comes amid growing tensions between the west and Russia over the right course of action to take in Syria.