Tyson Fury has vacated his WBO and WBA world heavyweight titles to deal with his “medical treatment and recovery”.
The Briton, 28, has admitted taking cocaine to deal with depression and could also lose his boxing licence on Thursday.
He has not fought since beating Wladimir Klitschko in November 2015 and has twice withdrawn from rematches.
“I now enter another big challenge in my life which I know, like against Klitschko, I will conquer,” Fury said.
He said it was “for the good boxing” and “only fair and right” to give up his belts.
“I won the titles in the ring and I believe that they should be lost in the ring, but I’m unable to defend at this time and I have taken the hard and emotional decision to now officially vacate my treasured world titles,” he said.
In a statement, Fury’s promoter Hennessy Sports said the decision would “allow him the time and space to fully recover from his present condition without any undue pressure and with the expert medical attention he requires”.
Mick Hennessy added that the decision was “heartbreaking”.
Uncle and trainer Peter Fury has said Fury will return “stronger” and “reclaim what’s rightfully his”.
Fury withdrew from his latest rematch against Ukraine’s Klitschko, scheduled for 29 October, because of mental health issues.
He then admitted in an interview with Rolling Stone magazine that he was taking cocaine to help deal with depression.
The British Boxing Board of Control (BBBofC) met on Wednesday to discuss that revelation, as well as other comments by Fury, and could decide to strip him of his licence to box.
The WBO and WBA had already said Fury could lose his titles because of inactivity.
Meanwhile, promoter Eddie Hearn has said a deal is “very close” for Britain’s heavyweight champion Anthony Joshua to fight Klitschko for his IBF belt and the now vacated WBA title.
It is thought New Zealand’s Joseph Parker and Mexico’s Andy Ruiz Jr could now contest the WBO title.