Kazakhstan's central bank governor Marchenko was put forward by Russia and a group of ex-Soviet states in May, but Finance Minister Alexei Kudrin later said the country's position could shift.
"There's a lot of information coming from different sources which is implying that there's agreement between G8 countries about support for Madame Lagarde," Marchenko said in an interview with Britain's Daily Telegraph newspaper.
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"If countries which together have more than 60 percent of the vote have agreed to support one candidate, then it's more or less a done deal," he said.
Lagarde is seen as the leading candidate in the IMF race, which also includes Mexico's central bank chief Agustin Carstens.
The IMF job fell vacant after former chief Dominique Strauss-Kahn was arrested on charges of sexually assaulting a hotel maid in New York. He has denied charges.
Russia has not officially supported Lagarde's candidacy, but
late in May Prime Minister Vladimir Putin said the French minister is "completely acceptable.
(Reporting by Karolina Tagaris)