The 40-year-old, whose younger brother Vladimir holds the IBF, IBO, WBA, and WBO belts, said he would focus on parliamentary elections in Ukraine after the fight against undefeated Charr and election to office could spell the end of his boxing career.
"Depending on the outcome of the elections (in October) I will decide on the future of my sporting career," said Klitschko in a statement.
"Holding a political office and being heavyweight champion at the same time are not compatible."
Klitschko has won 44 of his 46 professional fights and his last bout was a points victory over Briton Dereck Chisora in February.
He had said in March that his next fight would be against former WBA champion David Haye, who retired in October after losing his title to Vladimir in July 2011 but the much-awaited bout has failed to materialise on a number of occasions.
"Charr is young, hungry and undefeated," said Klitschko.
"He fears no one and always looks forwards. He will be very motivated against me and I will not make the mistake of underestimating him."
The Syria-born Charr has won all of his 21 fights since turning professional in 2005.