Former All Black Jonah Lomu wants countryman Sonny Bill Williams to focus on the upcoming World Cup, after which the pair can sort out a time to meet in the boxing ring, a British newspaper reports.

Lomu, 36, the Rugby World Cup all-time top try scorer is still stinging from Williams' refusal earlier this year to face him on the canvas, British newspaper The Daily Telegraph reports.

In June Williams turned down a chance to fight Lomu, saying the latter would not be a "credible opponent".

"It's a touchy subject but the offer is still there with his manager," said Lomu who admits to having spent his life training in boxing gyms and this December is planning to launch his amateur boxing career.

"For him to say I had no credibility and then fight someone on the sick (Williams ended up fighting Tongan Alipate Liava'a who, it transpired, was on sickness benefits at the time), well that's one sure way of ****** me off. I want to get him in the boxing ring one day," Lomu said.

"If he steps in the ring with me he will do so at his peril. I might not be a boxer as such but I know the sport and I can fight. If you hit me, I will hit you back so hard you will wish you hadn't.

"He should concentrate on winning the World Cup with New Zealand and perhaps we will sort it out afterwards."

Having officially retired from rugby in 2007, Lomu is now training for his boxing debut in Auckland on December 3 when he will compete in the charity event, Fight for Life.