LONDON, Sept 30 (Reuters) - Anthony Joshua said on Thursday he knew where he went wrong in losing his world heavyweight boxing titles to Ukrainian Oleksandr Usyk, and had learnt his lesson. Usyk took the Briton"s WBA, WBO, IBF and IBO belts on a unanimous points decision at London"s Tottenham Hotspur Stadium last Saturday. "I’ve watched the fight, analysed my preparations & identified my mistakes. I’ve learnt my lesson," Joshua posted on Instagram on Thursday. "Don’t worry about me. My spirit is strong!" A rematch is expected in February or March, with a possible world heavyweight unification fight between Joshua and compatriot Tyson Fury, the WBC champion, thrown into uncertainty. Fury"s promoter Frank Warren said on Monday he could not see it happening. read more His boxer, who will defend his title in a rematch with American Deontay Wilder in Las Vegas on Oct. 9, advised Joshua to take the fight to his opponent next time. "My advice to Joshua in the rematch is get stuck in, the best way he knows how. Put your best foot forward. Swing away, swing away," he said. "Joshua has to do what he"s got to do. I can"t say I"m interested because I"ve got "the Bronze Bomber" next. Whoever"s next? We"ll deal with them too." Fury rubbed in Joshua"s new status as a beaten champion by saying he had no interest in kicking people when they were down. "I like to pick on people who are doing well, who are successful, on top of their game," he said. "I don"t like picking on people who are down, probably at their lowest point, and probably mentally unstable after a loss after a long reign." Fury said he was ready for Wilder and reckoned his opponent was comfortably the best heavyweight out there.