American superstar Errol Spence Jnr has been branded “a punk” by Tim Tszyu and challenged to bet $50,000 on the result of Sunday’s WBO world title showdown.

Only days out from facing Tony Harrison for the WBO interim super welterweight championship, Tszyu has amped up fight week by taking the big stick to what he labels his “Team America” critics.

Watch undefeated Aussie superstar Tim Tszyu return to the ring for his biggest fight yet versus USA’s former world champion Tony Harrison for an Interim WBO Super Welterweight title LIVE Sunday March 12. ORDER ON MAIN EVENT ON KAYO SPORTS >

Despite being favoured against Harrison with bookmakers, a crew of big name US fighters have gone public to tip against Tszyu – among them undisputed welterweight king Spence and former two-division champion Shakur Stevenson.

Ranked among the top five fighters on the planet, Spence even took to Twitter recently and declared he will be wagering $10,000 on a Harrison upset.

Yet speaking with Fox Sports Australia this week, Tszyu labelled the undefeated US star “a punk” who would eventually be made to pay for his sledging.

Team Tszyu supporter and Sydney boxing manager Pete Mitrevski has also weighed into the debate, offering to bet $50,000 on Tszyu if Spence really wants to back his countryman.

“When Errol Spence initially tweeted about betting $10,000, I responded with ‘let’s make it 20K’,” said Mitrevski, who has worked with the likes of Paul Gallen, Harry Garside and now rising Aussie star Sam Goodman.

“But he’s quickly disappeared, though.

“Wants no part of that bet.

“But now in fight week, I’m willing to go up to $50,000.

“I’ve also spoken to Grant Palmer at Palmerbet, and he’s happy to take on Spence for whatever he wants to have on Harrison.

“So let’s see what Errol says.”

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Tszyu has also warned Spence — who is ranked No.4 in the world by Ring Magazine — that a showdown with the pair could happen within his next three fights.

Asked why the undefeated American would make such a big deal about betting against him, Tszyu shrugged: “The guy’s a punk – that’s why.

“And remember, this is the same person who also said Terrell Gausha was going to beat me in my last fight too. So what happened there Errol?

“I’ve never said anything bad about the bloke whatsoever.

“But for some reason, he just doesn’t like me.

“He’s Team America, I guess — that’s how they are.

“But these punks, they will all be put on notice.

“I’ve got a long future ahead of me and I’ll pin-point all of them one by one.”

So what chance Spence could simply be putting in the early groundwork for a future fight?

“Could be,” Tszyu grinned. “And that would make one hell of a fight.

“He’s definitely a good boxer.

“Which I respect.

“But I’d also welcome that fight with both hands.”

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Apart from Spence, former two-division champ Stevenson is also backing against Tszyu, saying recently: “Tony Harrison is going to beat him.

“I don’t think that Tim dude is that good.

“As long as Tony don’t get caught with a good shot (that would) hurt him, wobble him or get him outta there … it’s hard for anyone to beat Tony Harrison when he’s on his A game.”

However, Mitrevski has $50K that says different.

“Because Tony Harrison is not a puncher,” he said. “And if you’re not a puncher you aren’t beating Tim Tszyu.

“Timmy just works too hard, throws too many punches.

“He’s the ultimate pressure fighter … absolutely relentless.”

Already, Tszyu has revealed his blueprint for 2023 is to beat Harrison, unify the division against Jermell Charlo and then take on Spence in a superfight.

Better, manager Glen Jennings said, behind the scenes, work was already taking place to ensure that if everything goes as expected Sunday, Australia’s new world champ will not be on the sidelines for long.

Jennings also took a shot at Spence, saying: “Errol is one of these guys that spends an enormous amount of time having fights on social media, rather than in the ring.

“Although now there’s talk he will come up to Tim’s weight class, and we certainly hope he does.

“I know that’s a fight Tim would like.

“And depending on the circumstances, Harrison, Charlo, Spence would be a nice running order.

“We’d love to get Spence as soon as he comes up.

“And if Tim is the undisputed champion at that time, I’m sure Errol would love to have a crack at him, too.

“I actually think these bets, these little niggles, they give you an insight into what they might be thinking.

“(Laughs) Or maybe the guy just likes a bet? Who knows?”

Jennings also revealed that, while Tszyu was firmly focused on Harrison, he was already looking at what lay ahead if his client wins the interim strap.

“Tim certainly isn’t looking past Tony Harrison,” he stressed. “But we don’t ever want to see him waiting around for another 12 months like he has been, either.

“The Australian mentality, it’s to be No.1

“Fight the best.

“The Americans though seem to be hell bent on fighting on social media.

“If these guys could just get their acts together and sign a deal … it all just takes way too long.

“So that’s why we’ll be ready to roll the moment Tim disposes of Tony Harrison.

“We’ll be ready to move on with the next one quickly.”

Watch undefeated Aussie superstar Tim Tszyu return to the ring for his biggest fight yet versus USA’s former world champion Tony Harrison for an Interim WBO Super Welterweight title LIVE Sunday March 12. ORDER ON MAIN EVENT ON KAYO SPORTS >

So as for when Charlo will be ready?

“They’re being a little cagey, as they probably should be,” Jennings said.

“Will wait to see what happens in this fight.

“But I understand Jermell is out of his cast now and back doing some training.

“Obviously there is still some rehabilitation to go so it’s anyone’s guess … and I don’t think they will be too forthcoming just yet about when he will be ready.

“But we’re still hoping the injury repairs reasonably quickly so we can get on with it.”