Wladimir Klitschko has accused world heavyweight champion Tyson Fury of throwing boxing into disrepute.
The Briton has twice called off a fight against the Ukrainian, announced his retirement from the sport only to claim a few hours later that he was "going nowhere" , and admitted to taking cocaine.
Fury, the WBA and WBO champion, had been due to defend his titles against Klitschko in July but pulled out with an ankle injury.
The fight was then rescheduled for this month but postponed again due to an unspecified medical condition, with Fury making further headlines by telling Rolling Stone magazine he had taken to drinking and cocaine to deal with depression.
"Fury is dragging boxing through the mud," Klitschko told Bild.
With Fury not active at the moment, Klitschko is rumoured to be considering a bout against another British fighter, former Olympic champion Anthony Joshua.
Klitschko, who lost his titles to Fury in a surprise defeat last year, has been waiting for almost 12 months for a rematch.
"This just shows how unfair Fury is," Klitschko's manager Bernd Boente told the newspaper.
"He stalls with Wladimir. He blocks the world title."
Fury has also been charged with an anti-doping rule violation by UK Anti-Doping after a urine sample from February 2015 - nine months before his victory over Klitschko, showed traces of the banned stimulant nandrolone. He has denied doping.
The 28-year-old on Monday announced his retirement from the sport in an expletive-laden tweet, only to abruptly reverse the decision hours later, saying he planned to carry on fighting.
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