By Martin Domin Francis Ngannou warned Tyson Fury he would be making a grave mistake by picking a fight with him outside the ring. Former UFC champion Ngannou dropped Fury in his professional boxing debut last October en-route to a controversial points defeat. Despite having his hand raised, Fury endured the worst night of his career and was forced to postpone a showdown with Oleksandr Usyk two months later after being hurt by the newcomer. The Cameroonian will face Anthony Joshua in his second professional bout on Friday with a shot at either Fury or Usyk – and the undisputed title – on the l…