Sonny Bill Williams has rated this weekend's Super Rugby Final against the Sharks in Hamilton as the biggest game of his career.

The former Rugby League star played in the World Cup Final for the All Blacks and the Super Rugby Final for the Crusaders last year, but he has revealed that the showdown with the Sharks on Saturday will mean even more to him.

Williams explained that he has never felt as attached to any team as he does to the Chiefs for whom he will play his last game in the Final before jetting off to Japan to join the Panasonic Wild Knights on a lucrative one-year contract.

He told Fairfax media: "This is definitely right up there - probably the biggest.

"I've said it earlier in the year - I've played in a lot of teams but I guess the emotions I feel playing with the boys, especially after last week's win, are probably second to none. So, hopefully, we do win this week and this will definitely be right up there," said Williams.

The talented midfielder said that his biggest challenge this week will be to keep his emotions in check and remained focused on the task of claiming the Chiefs' debut Super Rugby title.

"They tend to eat you up and next thing you know you'll be sitting at home awake at night not being able to sleep so you've just got to push it all to one side and hopefully when the final hooter comes you can let it all out," he said.

Williams said that the Sharks have proven themselves to be worthy finalists and added that his side will have to raise their performance levels if they are to overcome the red-hot Durban franchise.

"The Sharks are in tremendous form, playing some superb footy, and we're going to have to play better than we did last week, so it's a big ask, but I'm confident we can do it," he said.

The All Black centre has been at the centre of speculation regarding his possible involvement in the first two matches of the Rugby Championship, and confirmed that he has spoken to All Blacks coach Steve Hansen about playing in the two Tests against Australia, but added that it would only be possible with the blessing of the Wild Knights who he is due to join after the Super Rugby Final.

"I just had a quick chat with Steve [Hansen] and he told me about their situation. I said, of course I'd love to [play] if all the things are right on the Japanese front and it's worked out well.

"But that's probably the only time I've talked about it.

"You guys [the media] have made a big deal about it, but for me, my heart, soul and mind is definitely with the Chiefs. One more week and then I'll worry about that," he said.