Anthony Joshua says he has "learned his lesson" following his defeat to Oleksandr Usyk last weekend.
The former IBF, WBA and WBO champion relinquished his titles after an inspired performance by his Ukrainian opponent at the Tottenham Hotspur Stadium.
Joshua failed to recover from a slow start and subsequently slipped to his second defeat in four fights, with Usyk prevailing after 12 rounds in a unanimous points decision to maintain his unbeaten record as a professional.
The two fighters are reportedly set to do battle once more in early 2022 after the dethroned heavyweight champion "activated in principle" a rematch clause.
Now 24-2, Joshua insists he knows where he went wrong as the Briton looks to reclaim his belts.
Posting on Instagram, he told his 13 million followers: "I've watched the fight, analysed my preparations and identified my mistakes.
"I've learnt my lesson. Thanks for sending love and checking in.
"Don't worry about me. My spirit is strong!"