Sonny Bill Williams suits up for his Sydney Roosters press conference on Tuesday.

Sonny Bill Williams suits up for his Sydney Roosters press conference on Tuesday. Photo: Brendan Esposito

Anthony Mundine has welcomed Sonny Bill Williams's return to rugby league, but says his friend's blossoming boxing career will improve a lot more once he concentrates full-time on the sport.

Former Canterbury star Williams, who walked out on the club in July 2008, will return to the NRL next year with ? Sydney Roosters.

He enjoyed Super Rugby and Rugby World Cup wins during his time in New Zealand and also had a union stint in Japan while continuing his career as a professional pugilist.

Williams has accumulated a 5-0 record as a heavyweight boxer, though his fight with South African veteran Francois Botha has been rescheduled to next year after a pectoral-muscle injury he suffered in Japan.

In 2000, Mundine quit rugby league to follow in the boxing footsteps of his famous dad and former middleweight world title contender, Tony Mundine.

'The Man' has gone on to win national and world title belts but has never felt the compulsion to juggle different codes.

Unlike Williams, Mundine, who will challenge IBF middleweight world champion Daniel Geale on January 30, opted to focus on boxing rather than work it around football commitments.

"I dabbled in it [boxing, with four amateur fights], a little bit when I was playing footy, but I was mainly focused on my football career, and I didn't really plan back then to juggle it," Mundine, aka 'Choc', said on Wednesday.

"It worked out that when I quit the sport, I wanted to just focus solely on boxing and I think that's the best way you can get the best out of yourself as far as fighting.

"But Sonny is an incredible athlete, an incredible footballer and he's doing great as far as juggling the three [rugby union, rugby league, boxing] because it's hard, very hard.

"Maybe there's a point down the track, I don't know if Sonny wants to but it's up to him, that he wants to go full-time boxing. I think he'll improve a lot more in every department in his boxing skills," he said. AAP