Kell Brook says he will announce his retirement in the ring if he loses to Mark DeLuca on 8 February.
Brook, 33, will face the American after a 14-month spell out of the ring.
Sheffield’s Brook has endured a testing period since 2016, having broken both eye sockets and given up his world welterweight title.
“This last chapter of my career, I’m giving it my all,” Brook said. “If I get beaten I can walk away with my head high, knowing I have given everything.”
He told the 5 Live Boxing Podcast: “If I get beaten by DeLuca, I will announce my retirement in that ring. If I can’t beat him, what am I doing?”
He now feels that if he were to retire – even as a former world champion – he would not feel fulfilled with his achievements. BBC Sport boxing correspondent Mike Costello says the admission is “staggering”.
Brook has said he was “a mess” in the aftermath of losing his IBF world welterweight title to Errol Spence Jr at Sheffield United’s Bramall Lane in 2017, and resorted to “drinking too much” because he felt down.
He turned to counsellors and said he “poured my heart out to them”.
Ask why he now feels happy, Brook said: “I think it’s age. And I think it’s realising the window of opportunity is very small now. I have realised I have been cheating myself and it is me who pays for it. So I am going to give myself the best opportunity to give my all.
“It’s me who walks in my shoes. I know that I have never been 100% but now I am 100%. But I am not a young buck any more and I have to look after myself. I have to go to bed at night, not cut corners, do it by the book.
“Obviously I was young and thinking I could do it all as a world champion but I am sitting here now and the penny has dropped. I have seen the light now.”
DeLuca has been beaten just once going into the Sheffield Arena bout.
Brook has lost twice in a 40-fight career, during which he travelled to the US to land a shock world-title win against Shawn Porter in 2014.
His trainer Dominic Ingle added: “I always say with fighters that they all come to the realisation that after 30 it all starts to fall into place.
“The mind gets a bit smarter. Whether the body can keep up is another thing. It’s a big fight for Brook and he will decide whether he can go on to bigger things.
“Kell was destined for big things. It has always been a case of keeping him on track as he has had a lot of people around him hyping him up.
“He has been out well over a year and we just don’t know with his age whether he is going to do it. I think 2021 might be the last year. He has been rejuvenated and we have to ride this wave as long as we can.”
‘A forgotten man in hellish holes’ – analysis
BBC Sport boxing correspondent Mike Costello: It is hard to escape the notion that Brook has become the forgotten man of British boxing.
I remember being at one of the very first news conferences he was at after joining forces with promoter Eddie Hearn. People were saying ‘this is the special one’ and ‘this is a very special kid’.
He went on to win the British title, then, in one of the single best wins ever by a British boxer, he beats Shawn Porter in the US. That was one of the great wins.
BBC Radio 5 Live analyst Steve Bunce: Saying he is a forgotten man is not too strong.
He turned pro at 18 and got £300 for his first fight. For his third fight, he didn’t even get paid. He started his career facing obscurity and hardship.
I’ve had him on a dozen things and he’s talked about walking away. He has been in some black, hellish holes. I have to be honest, by about the summer of 2017, I thought it might have been all over for Brook.