Tszyu senior was set to fly from his home in Russia to be at his son's fight against American Sebastian Fundora on Saturday (Sunday AEDT), when he will try to add the super welterweight WBC belt to his WBO title strap.

If Tim succeeds he and Kostya will join Leon and Corey Spinks as only the second father-and-son duo to become unified world boxing champions.

Hall of Famer Kostya Tszyu fought five times in Las Vegas, including his famed 2001 KO of Zab Judah. However, Tim will become the first Australian-born fighter in history to headline a US pay-per-view.

But Tim said his dad, who has only seen him fight live once before - back in 2016 on his professional debut - would miss the biggest bout of his career.

He wasn't sure if it was visa issues around entering the US from Russia.

"We found out last night he's not coming," Tszyu told AAP ahead of his Tuesday training session in Las Vegas.

"I'm not too sure what the issue was - it's just a bit hard with everything going on in Russia, so they decided to stay."

Tszyu said he wasn't bothered his father wouldn't be in his corner for such a massive occasion.

He previously described Kostya's surprise appearance at the Sydney fight eight years ago as "chaotic" and "out of control".

Kostya's decision keeps things simple for his oldest son, who has already had to deal with a change of opponent with just 12 days' notice following the injury to Keith Thurman.

"He's only come to watch me once before so I'm used to it," said Tim, whose record is 24-0 (17KO).

"It would have been the unknown if he came down."

Victory on Sunday will set up a mega-fight with pound-for-pound king Terence Crawford, who last week announced he would exercise his right as WBO welterweight champion to be named mandatory challenger for the winner of Tszyu versus the 197cm Fundora, who has a 21cm height advantage.

The 29-year-old Sydney slayer is in line for $US10 million ($15.3 million) to enter the ring with Crawford (40-0, 31KO).

Fundora was on track to a world title before he was knocked out by Brian Mendoza - the same fighter Tszyu downed by unanimous decision in his last ring outing in October 2023.

Tsyzu said after spending a week sparring against boxers who fit the towering mould of the Californian, he was confident he had Fundora's measure.

While body blows seem the obvious tactic, Tszyu said Mendoza had proven there were other ways to bring down his lanky opponent.

"When you get knocked out like that, your chin is vulnerable and you're not the same fighter as you were, so hopefully that's something I can exploit," Tszyu said.

"I'm going to knock his spark out, that's the plan, I will keep it quite simple,"

"It's been a long, long prep, so it's been a long road, so it's good to be at the final stages."

Australian Associated Press