Towering Briton Anthony Joshua is fighting for his career on Saturday against Ukrainian  Oleksandr Usyk, who can boost the morale of his compatriots in war-torn Ukraine by retaining his world heavyweight belts in Saudi Arabia.

Joshua, 32, has much on the line as he strives to become a three-time world champion and perhaps spark fellow Briton Tyson Fury into performing another U-turn on retiring and set up a blockbuster unifying title bout.

Back-to-back defeats by Usyk, who outboxed him in London last September, would be a career-crippling setback for the 2012 Olympics super heavyweight gold medallist who also crashed to a surprise TKO against Andy Ruiz Jr in 2019.

Usyk, the undefeated former cruiserweight world champion, won on an unanimous decision in only his third professional fight as a heavyweight.

In response, Joshua has recruited respected trainer Robert Garcia and is hinting at a more aggressive approach against the mobile and unpredictable southpaw.

"It's all about the fight," Joshua said at the weigh-in, where he maintained his 10-kilo (22 pounds) weight advantage over Usyk.

"I'm just ready for 12 rounds, 100 percent. Anything shorter than that, it's a bonus."

Stopping the 19-0 Ukrainian would be quite a feat.

Usyk has never been knocked out in 129 outings, including in his outstanding 95-15 amateur career which like Joshua saw him win gold at the 2012 Olympics in the heavyweight division.

He has knocked out 13 opponents since turning pro.

The 35-year-old also has the enormous incentive of fighting for a country that has been defying a Russian invasion since February.

The bout will be screened free of charge across Ukraine.

"We had enough time to study each other," Usyk said this week. "We were born to compete for life, for belts, for everything. The one who does not compete, does not win."

'People wanted him to fight' 

Following the invasion Usyk volunteered as a soldier and returned to Ukraine before being advised by senior officials to accept the rematch against Joshua.

"He was in touch with high-ranking military officers and he visited the hospitals with injured soldiers," said his promoter, Alexander Krassyuk.

"In every conversation he heard words of blessing and support to take the rematch. People wanted him to fight."

Usyk appeared in Cossack dress and sang a resistance song on stage in the fight's build-up, taking inspiration from a surge in nationalist pride following the invasion.

Juggling, marathon swims, 100-kilometre (60 miles) bike rides and even a coin-tossing party-piece -- he threw four coins into the air at the same time and caught them separately as they fell -- have all been part of the preparations for the charismatic pugilist.

The second world heavyweight fight in Saudi Arabia, after Joshua took his revenge against Ruiz in late 2019, has been accompanied by accusations of Saudi "sportswashing" -- using sports events to detract from its human rights record.

This week it emerged that a Saudi woman had been jailed for 34 years for posting tweets critical of the government, a case that the United Nations called "appalling".

Also on Saturday's card, Somali-born Briton Ramla Ali will fight the Dominican Republic's Crystal Garcia Nova in the first women's professional boxing match in the conservative kingdom.