Tyson Fury faces Oleksandr Usyk in the first undisputed heavyweight fight for a generation on Saturday with bad blood boiling after a tempestuous clash at the weigh-in.

The two undefeated fighters had previously been respectful in their comments but tempers flared on Friday as Britain's Fury shoved Usyk and swore angrily at the Ukrainian.

It adds extra spice to Saturday's classic encounter at Riyadh's Kingdom Arena, the first undisputed heavyweight bout since 1999 with the winner taking all four major belts.

"We're ready to rock and roll, so fireworks tomorrow night. I'm going knock (him) spark out," fumed Fury.

"I'm coming for his heart, that's what I'm coming for. (Forget) his belts. I'm coming for his heart. He's getting it tomorrow, spark out!"

Earlier this week, Fury's father John headbutted a member of Usyk's entourage and was seen with blood streaming from a cut on his forehead.

The fighters can join the likes of Muhammad Ali and Mike Tyson by becoming undisputed champion, a feat not achieved since Lennox Lewis beat Evander Holyfield in 25 years ago.

With four boxing sanctioning bodies, up from three, the winner will unite Fury's WBC title with the IBF, WBA and WBO belts held by Usyk, and will be recognised as the greatest of this era.

- Too close to call -

The highly-anticipated match has been long in the making. Originally announced for February, it was postponed after Fury suffered a cut in training.

With the hype going into overdrive, there is the potential for anticlimax with some commentators expecting a cagey fight with Fury on the defensive.

The 6ft 9ins (2.06m) "Gypsy King", who struggled to a split decision against ex-MMA fighter Francis Ngannou in October, has shed excess pounds, weighing in at 262lb, and looks leaner and light on his feet.

Southpaw Usyk, formerly an outstanding amateur and the undisputed cruiserweight champion, gives up six inches in height and seven inches in reach.

But the quick, mobile Ukrainian has triumphed against bigger opponents before, beating the towering Anthony Joshua twice.

Predictions are split over the outcome, with some tipping the rangy, enigmatic Fury and others backing the supreme skills and fitness of Usyk.

Both fighters have impressive records -- Fury is 34-0-1 with 24 knockouts, Usyk 21-0 with 14 KOs -- and engrossing back stories.

Fury, who comes from a line of bare-knuckle boxing Irish Travellers, has bipolar disorder and has battled alcoholism, cocaine abuse, depression and thoughts of suicide, announcing his retirement twice.

The 35-year-old famously upset another champion Ukrainian, Wladimir Klitschko, in 2015 and fought a memorable trilogy against America's Deontay Wilder.

Usyk, 37, who briefly served as a soldier after the Russian invasion, cleaned up as an amateur and won an Olympic gold medal in 2012.

After then turning pro, he was the unified cruiserweight champion within 15 fights and claimed Joshua's belts in just his third outing at heavyweight.