Five-weight boxing world champion Terence Crawford says he is "walking away as a great with nothing else left to prove" after announcing his retirement at 38.

The American, who finishes with a perfect record of 42-0, made history in September when he beat Saul 'Canelo' Alvarez to become the first male fighter in the modern era to hold undisputed titles in three weight divisions.

That will now go down as Crawford's last fight, having started his professional career in 2008 with a victory over Brian Cummings.

His future had been debated since he beat Canelo to become the undisputed super-middleweight champion, adding to titles at lightweight, light-welterweight, welterweight and light-middleweight.

In a post on his YouTube channel, external, Crawford said "every fighter knows this moment will come, we just never know when".

He added he had "nothing else to prove" in the caption, external to his video on social media.

"I spent my whole life chasing something," said Crawford. "Not belts, not money, not headlines, but that feeling, the one you get when the world doubts you but you keep showing up and you keep proving everyone wrong.

"This sport gave me everything, I fought for my family, I fought for my city, I fought for the kid I used to be, the one that had nothing but a dream and a pair of gloves, and I did it all my way.

"I gave this sport every breath I have, every spar, every triumph, every ounce of my heart. I've made peace with what's next. Now, it's time. Thank you."

Omaha-born Crawford had 31 knockouts in his 42 fights, which included WBO welterweight title wins over Britons Amir Khan and Kell Brook.

Steve Bunce, BBC Radio 5 Live boxing commentator

Terence Crawford is not the first fighter to suddenly vanish when he's at his peak.

And guess what - wait for it - he won't be the first fighter to suddenly come back after vanishing. I think he'll come back.

And there's one big problem - when you're Terence Crawford, and your last fight was as the underdog, beating the great Saul Canelo Alvarez, in front of 70,000 people outdoors in Las Vegas, that's an awful lot of success.

But what's more, he got millions and millions and millions for it.

It's really hard to fight after that, for 10% of that or half of that, even if it's 10 million dollars. If you've made 30, 40 or 50, 10 million is not very much money.

So will he come back? I think so.

If he stays retired, it'll be one of the greatest retirements in boxing history.

Unbeaten, champion at all those weights, untouchable, regal, and he goes. That's what I'd like to see.