Sonny Bill Williams is keeping everyone guessing about his future plans after playing a pivotal role in the Sydney Roosters' National Rugby League grand final victory over Manly at the weekend.

The dual rugby international superstar forward was influential in the Roosters' second-half comeback to overhaul the Sea Eagles and win their 13th title 26-18 in Sydney on Sunday.

But he has been reticent about divulging his plans amid reports that he is considering a return to the Super Rugby champions Waikato Chiefs, which would put him in the frame for a second World Cup tilt with the All Blacks in 2015.

Williams, 28, was asked the burning question straight after Sunday's full-time siren but he ensured his next career move would not overshadow the Roosters first NRL premiership since 2002.

"In a couple of weeks," he told reporters asking of his future plans. "I'm just happy to be in this group of young men (Roosters team).

"I'm blessed to have been in a few good teams over the year and this one is no different."

Backrower Williams made an uninspiring start to an absorbing contest, yet when the showpiece was in the balance he helped engineer the key momentum shift.

A flick pass to stand-off James Maloney was the catalyst for centre Shaun Kenny-Dowall's levelling the scores at 18-all before Maloney kicked the conversion.

Williams also made crucial ground before Maloney's grubber kick culminated in a spectacular diving finish by Michael Jennings, seven minutes from time.

Williams was also vague on his prospects of representing the Kiwis at this month's rugby league World Cup in England and Wales.

The Kiwi squad is scheduled to be announced on Tuesday.