Conservative MP Tim Yeo has pulled out of the race for the Conservative leadership, and said Ken Clarke was the man to lead the party.
Mr Yeo urged Conservatives to support Ken Clarke
Mr Yeo said: "The most important consideration for the party is who can lead us to victory.
"In my view unquestionably the most likely person to defeat Labour and to see off the threat from the Liberal Democrats is Ken Clarke."
Another candidate, David Davis, has played down the threat from Mr Clarke.
In his statement released on Saturday, Mr Yeo said: "I therefore urge Ken to enter the contest at the earliest opportunity.
"I hope my supporters and colleagues, including those who are themselves still thinking of running for the leadership, will follow my lead and back a winner."
Mr Yeo, who represents South Suffolk, said Mr Clarke was "the best qualified and most popular of all the potential candidates".
Former chancellor Mr Clarke used a recent interview to say the euro had so far been a failure - thought to be a move to counter fears within the party of his pro-EU stance and past support for the single currency.
Mr Yeo denied the comments amounted to a U-turn by Mr Clarke, who unsuccessfully ran for the leadership post in 1997 and 2001.
"Five years ago we did not know it was going to be a failure," he told the BBC. "People make judgements. Sometimes they are right and sometimes they are wrong. He's made more right judgements than most."
Mr Yeo said "one of the obstacles" surrounding Mr Clarke's leadership credentials has now been removed.
The battle for the Tory leadership began after the general election, when Michael Howard announced he was standing down after Labour's third victory.
Mr Davis is tipped as the frontrunner by bookies
In a comment last week over the length of the contest, which has not-yet officially started, Mr Davis said: "It's a race where the horses spend more time in the paddock than on the racecourse."
Earlier last week supporters of another would-be leadership challenger, David Cameron, said there would be no chance of a "dream ticket" deal with Mr Clarke, who has unsuccessfully stood for the leadership twice before.
Other potential candidates include Liam Fox, David Willetts, Theresa May, Sir Malcolm Rifkind and Andrew Lansley.
The rules will not be finalised for the leadership contest until late in September, although Conservative MPs have already voted for a system where they, rather than party members, choose the leader.