Chancellor George Osborne says he will not compete in the Conservative leadership battle.
Writing in The Times this morning, Osborne says he accepts the results of the EU referendum but that he cannot give "unity" to the Conservatives.
He says: "As for my own future, I will not be a candidate in the Conservative leadership election to come.
"It isn’t in my nature to do things by half-measure, and I fought the referendum campaign with everything I’ve got. I believed in this cause and fought hard for it. So it is clear that while I completely accept the result, I am not the person to provide the unity my party needs at this time.
"Instead, as Chancellor, I will be 100 per cent focused on providing the economic stability and reassurance Britain needs. And I will do all I can to support the new prime minister in bringing our party back together and tackling the country’s challenges."
Osborne add: "Britain has a great task now to make its new position in the world work. Let’s be confident that whatever difficulties confront us as we negotiate it, we do so from a position of hard-won strength.
"As has always been the case in our history, it is at its moments of greatest challenge that our country must demonstrate its greatest resolve."
Osborne's move leaves Boris Johnson and Home Secretary Theresa May as the most likely frontrunners.
Last Friday Prime Minister David Cameron announced he would resign in the Autumn following the vote to leave the EU.