Ben Wallace, the Defence Secretary, was one of the favourites by bookies to succeed Boris Johnson. He has now said that he will not be running for the Conservative Party leadership.
He stated that he is focusing on his current job and "keeping the great country safe" in a Twitter statement.
He wished the candidates luck and said that he hoped they would "return to focusing on issues quickly".
Former Chancellor Rishi Sunak is the most prominent candidate to succeed Mr Johnson.
It appeared that Mr Wallace was in a strong position, as he was topping surveys by Conservative Home and being the favourite of the bookmakers.
It will be interesting to see which candidates he endorses. This is likely to give them a huge boost in their campaign.
On Friday, Mr Sunak announced his campaign by stating that "someone must grasp this moment and take the right decisions."
On Tuesday, his resignation from the cabinet triggered a mass walkout by ministers, which forced Boris Johnson out of office as Tory leader.
Many Tory MPs, including Oliver Dowden and Mark Spencer, have supported Mr Sunak's campaign.
A No 10 source said that Mr Sunak was disappointed in Downing Street.
They said he had a "short mind", and added: "It was the prime minster who trusted him, and gave him a top position when he was a junior Minister.
"The prime minister supported him to the end. It is a shame that it was not reciprocated."
To a series of supportive messages on social media by Tory MPs Mr Sunak tweeted: "Thanks. Thank you so much for your support.
"Together, we will restore trust and rebuild the economy to reunite the country."
Johnson stated that he will remain in Downing Street until a successor has been chosen.
Kemi Badenoch, former Equalities minister, became the latest Conservative MP to join the race. She was confirmed by the Times.
She stated that she wants a limited government and to tell the truth.
Tom Tugendhat, a senior Conservative backbencher, and Suella Braverman, Attorney General, have both launched leadership bids.
In the Daily Express, Ms. Braverman stated that she would lead by bringing in large and rapid tax cuts.
After his announcement, Mr Tugendhat stated to BBC South East that he had served 10, 15, years in the military, six, seven years in Parliament and would like to return because he believes this country is important.
"I believe the innovation and opportunities that these people show every day is what we should champion and make that new deal because there is a new deal in Britain.
