LONDON -- Tyson Fury has decided to "walk away" from boxing, only three days after saying he was returning to the sport.

Fury turned 34 on Friday and posted a message on social media saying: "Massive thanks to everyone who had an input in my career over the years & after long hard conversations (I've finally) decided to walk away & on my 34th birthday I say Bon voyage."

That seemingly puts Fury back into retirement, after he announced on Tuesday that he was returning to boxing in order to set up a fight against Derek Chisora, a fellow Briton whom he beat twice early in his career.

That announcement had sparked speculation that Fury, the reigning WBC heavyweight champion, was targeting a possible unification bout against the winner between Oleksandr Usyk, the reigning WBA, IBF and WBO titleholder, and Anthony Joshua, who are fighting on Aug. 20 in Saudi Arabia.

Fury did not give a reason for his apparent change of heart.

The undefeated Fury initially said after his win over Dillian Whyte at Wembley Stadium in April that he was retiring from the sport.