Wladimir Klitschko has concerns about Alexander Povetkin meeting him in Moscow on October 5.
Povetkin has withdrawn twice from fights against the Ukrainian, whose WBA title will be at stake.
Klitschko, 37, was due to fight Povetkin in 2008, but the Russian injured an ankle in training. Two years later the now 33-year-old Povetkin pulled out of a second bout when his father died.
October's clash at the Olimpiyski Arena will determine who is the WBA champion. The fight details were decided recently after Klitschko insisted that the drug testing is done in Germany.
Klitschko, who faces his 24th title fight, has told Hamburg's Morgenpost he was "cautious in regards to Povetkin.
"We twice agreed to fight and he withdrew. With Povetkin, you never know what happens," said Klitschko, whose WBO, IBF and IBO titles will also be on the line.
Klitschko has been the WBA "super" champion since 2011 when he beat Britain's David Haye. Povetkin, who holds the regular belt, won the Olympic heavyweight title in 2004. He is undefeated, boasting 18 knockouts in 26 fights.
Klitschko, who won Olympic heavyweight gold at the 1996 Atlanta Games, says he hopes the Russian does not cancel for a third time.
"He really listens to what other people say. I hope people tell him that he should fight," said Klitschko, who has 51 knock-outs in 60 wins. The last of his three defeats was nearly a decade ago.
Klitschko stands to make a career-high $17 million from the fight and Povetkin $5.7 million.
The date of the fight was moved back after lengthy negotiations with the Klitschko camp who refused to have the Russians take care of the drugs testing. It will be conducted by Germany's National Anti-Doping Agency (NADA).
"I have a name to lose, which is worth far more than the money I get from this fight," said Klitschko. "I can't afford any inconsistencies."