Northampton South MP Andrew Lewer has thrown his support behind the former Mayor of London in the Tory leadership race.
Boris Johnson emerged as the clear frontrunner to succeed Theresa May as the Conservative leader and next Prime Minister, following the results of the first round vote on Friday.
Mr Johnson, who was Foreign Secretary between 2016 and 2018, did not take part in a live televised leaders' debate over the weekend.
Critics of the former mayor say he is a populist who orchestrated Brexit with a now infamous battlebus slogan - that turned out to be a false claim about the cost of immigration to the NHS.
But fellow Leave supporter Andrew Lewer has now opted to back Johnson in the leadership race.
The Northampton South MP tweeted yesterday: "@BorisJohnson is supporting @EstherMcVey1 #BlueCollarConservative policies as well as being determined to deliver a proper Brexit. He has my support!"
Very few social media users responded to the announcement positively.
"You are the unscrupulous following the unscrupulous," said one commenter among 73 on Twitter. "We deserve an honest, industrious, principled PM ...Boris is way off the mark."
Mr Lewer's Northampton North counterpart Michael Ellis has yet to publicly back a candidate in the race.
Kicking off his leadership campaign last week, Johnson positioned himself as the candidate most likely to deliver Brexit.
He said: "We cannot ignore the morass at Westminster where parties have entered a yellow box junction, unable to move forward or back, while around the country there is a mood of disillusion, even despair, at our ability to get things done.
"The longer it goes on, the worst the risk that there will be serious contamination and loss of confidence because the people of this country deserve the best from their leader."
Ending his speech, Johnson told the crowd he wanted to do what he did as the mayor of London to the whole country.