Anthony Joshua says he has "learnt my lesson" after losing his world heavyweight titles to Oleksandr Usyk in London at the weekend.

Usyk outpointed Joshua on all three judges' scorecards as he wrested the WBA, IBF and WBO titles away from the British boxer in front of a crowd of more than 66,000 at the Tottenham Hotspur Stadium.

Joshua cut a surprisingly relaxed figure in the early hours of Sunday as he gave his initial thoughts on just the second defeat of his 26-fight professional career despite having greater height, reach and weight than his Ukrainian opponent. 

In a social media post on Thursday, the 31-year-old said: "I've watched the fight, analysed my preparations and identified my mistakes. I've learnt my lesson.

"Thanks for sending love & checking in. Don't worry about me. My spirit is strong!"

Both camps are keen to activate a rematch clause, with Usyk hoping to take on Joshua in front of his home crowd in Kiev, although Eddie Hearn, Joshua's promoter, suggested a second fight would likely take place in Britain again on economic grounds.

Joshua's defeat has scuppered hopes of a "Battle of Britain" unification heavyweight title clash with Tyson Fury.

Fellow British heavyweight Fury defends his WBC title when he meets Deontay Wilder in Las Vegas on October 9 -- the third meeting between the boxers following a split-decision draw and a victory for Fury.

"My advice to Joshua in the rematch is get stuck in the best way he knows how, put his best foot forward and swing away, Jack, swing away," Fury said on Wednesday.

"Was I absolutely wounded that (Usyk) won? Yes I was. I was hoping Joshua could win the fight, but he couldn't -- and that's none of my business.

"The only thing I'm bothered about is beating Deontay Wilder, and that's the most dangerous heavyweight out there. In my opinion, Wilder beats Joshua, Usyk, all the rest of the division, comfortable -- but he cannot beat me."