Ian McCullough AAP: More than four years after walking out on Canterbury, Sonny Bill Williams refused to offer an apology to the club after being unveiled as a Sydney Roosters player on Tuesday. The World Cup-winning All Black will turn out for the Roosters for the 2013 campaign having agreed a lucrative one-season contract with the NRL club. Williams admitted he only agreed to come back to the game he controversially quit midway through the 2008 season because he was honouring an agreement made with Roosters chairman Nick Politis three years ago. However, he was less forthcoming when asked whether he should say sorry to the Bulldogs and their supporters for his actions, which stunned the game when he boarded a flight to London to sign for French club Toulon - 48 hours before his side was due to face St George Illawarra. "Today is about me signing with the Roosters and that's what I'm going to stick to," Williams told a packed media conference on Tuesday. "There will probably be a time and place and we'll cross that bridge when we get to it." Williams, whose right shoulder was in a sling following surgery for an injury sustained during his $1 million stint with Japanese rugby outfit Panasonic last month, said he was unconcerned about any possible backlash from rival supporters next year. "I can't dwell on negatives. I have a one-year deal with the Roosters and there is big pressure," he said. "I have to get my shoulder right, and if I dwell on all the negatives then I won't be able to sleep at night." Asked to respond to claims from former Bulldogs teammate Hazem El Masri that he should not be allowed to return to the NRL, Williams said: "Haz is entitled to his opinion and that's all I have to say." Williams has enjoyed great success in rugby over the last two years, helping the All Blacks win the 2011 Rugby World Cup, then the Chiefs to a first Super Rugby crown this year. He also embarked on a boxing career, which he will put on hold during the NRL season, but hopes to get back in the ring before joining up with his new teammates in February - less than a month before the season kicks off. However, the 27-year-old said he would have to prove himself worthy of a place in the Roosters back-row and admitted it would be a big challenge for him to continue where he left off when he last played league, having been an outside back in rugby. "I'd love to say I'll slide straight in and pick it up straight away but it's going to a tough challenge," he said. "The biggest challenge will be the contact area. I was out wide kicking stones sometimes with the pretty boys in the backs. "It'll be tough if I move back into the forwards. There's going to be some big boys running my way." "A lot of people will be writing me off. Every time I step on that field there will probably be a target on me. I'll have to use my twinkle toes a bit." One obstacle that could hinder Williams' progress is the NRL's plans to outlaw the shoulder charge. Williams was the best exponent of the art during his time with the Bulldogs, and in the most delicious of ironies, the man chairing the shoulder charge review committee is new Roosters CEO Brian Canavan. "I've talked to him about that and told him to go easy," Williams quipped.