Oleksandr Usyk has issued a warning to Anthony Joshua that he may not get the chance of avenging his two defeats if he defeats Tyson Fury to become the undisputed heavyweight champion. The wait is nearly over for Usyk and Fury to step into the ring for this century’s first heavyweight unification fight after the original bout was postponed. Fury suffered a cut above his eye earlier this year that pushed the fight back to May 18. But both boxers arrive in Saudi Arabia this week with just days until they go face-to-face in the ring. As part of the contractual agreement for the fight, a rematch w…