FRANCOIS Botha will need to knock out Sonny Bill Williams to win Friday’s big fight.

The ageing South African heavyweight takes on the former All Black ingenue for the World Boxing Association’s international title in Brisbane at 10am on Friday.

Thinus Strydom, who has promoted most of Botha’s fights, believes this is the only way the South African will get the decision against unbeaten Williams.

Botha, 44, is a very experienced former International Boxing Federation and World Boxing Federation champion who should teach the 27-year-old Williams a lesson, probably ending the rugby star’s boxing career before it really gets off the canvas.

Botha boasts huge experience from 60 fights with 48 wins (29 knockouts ), eight defeats and three draws, to Williams’s five wins (three knockouts).

Speaking from Australia on Monday, Strydom said his charge needs to knock out Williams as winning on points in a foreign country was near impossible.

"Sonny Bill is young and is also a hot favourite," said Strydom. "So there is a lot of interest is him.

"But I am confident that Botha will knock him out. He is in excellent shape — the best ever … Botha must have lost about 10kg-15kg and that shows how serious he is about this fight. He is aware that a loss will affect a fight that is on the cards for Dubai.

"Sonny Bill’s people think that Botha is too old at 44 and his legs won’t carry him throughout 12 rounds," said Strydom. "But they are making a big mistake because even the likes of Mike Tyson and Wladimir Klitschko struggled before they stopped him."

He described Botha as the first genuine heavyweight opponent for Williams. "I am not running him down but let us wait and see how he reacts when he gets caught by a fully fledged heavyweight boxer like Francois.

"I’ve been with Botha for many years. I have seen him win and lose some of his fights. I have seen Botha being overweight, but still putting him flat down has not been that easy.

The man has got experience and he knows how to protect himself inside the ring. Losing to Sonny Bill is something I don’t even want to entertain, not when Botha is as fit as he is."