The New Zealand centre was hit with a ban when he appeared before a three-man judicial panel in Wellington on Sunday, after he received a 25th-minute red card from French referee Jerome Garces following a shoulder charge into Lions wing Anthony Watson's head during the second Test.
Sonny Bill Williams to miss deciding Lions Test after being hit with four-week ban
New Zealand centre Sonny Bill Williams has been suspended for four weeks after he was sent off in Saturday's second Test defeat against the British & Irish Lions.
Williams received a 25th-minute red card from French referee Jerome Garces following a shoulder charge into Lions wing Anthony Watson's head at Westpac Stadium.
And Williams was hit with a ban when he appeared before a three-man judicial panel in Wellington on Sunday, with the New Zealand Rugby Union announcing a verdict that means he misses next weekend's Test series decider.
Ahead of Williams's hearing outcome, the All Blacks called up centre Malakai Fekitoa to their squad ahead of the Lions clash in Auckland next weekend.
But the loss of Williams will be a major blow as New Zealand look to prevent the Lions from recording a first series victory over them since 1971.
Speaking in Wellington before the hearing, New Zealand coach Steve Hansen said that double World Cup winner Williams knows he let the All Blacks down with his sending off.
Williams was the first All Blacks player for 50 years to be sent off in a Test match, only the third of all-time, and first in New Zealand.
"Look, he's disappointed, not for himself, he accepts he has made a mistake," Hansen told reporters in Wellington.
"He is disappointed because he let the team down.
"One of our biggest mantras is the team comes first, and he knows he has let the team down, but we can't go back and change it.
"People make mistakes. It's a fluid game, a fast game and a physical game. Unfortunately, he's made a mistake and we've got to move on from it.
"Sonny has paid a big price and the team has paid a big price for him making a mistake, and we have to wear the decision. That's just the way it goes. Let's move on and talk about how good a Test match it was."
The Lions' 24-21 victory consigned New Zealand to a first defeat on home soil since 2009, ending a 46-match unbeaten run, while the All Blacks have not lost successive Tests for six years.
"No-one likes losing, but going to bed and going to sleep doesn't change the result," Hansen added.
"We've got to go to Auckland and we've got to go to prepare for a Test match. Does it make next Saturday a little bit more exciting than if we had won last night? You bet it does. We've got a real challenge on our hands, so that is exciting.
"I thought we were almightily courageous. Did we play well? Debatable. I think we can play smarter, but we certainly showed a lot of ticker and a lot of heart.
"I am very proud of our guys. They hung in there against a quality side and had a chance of winning the game. They never gave up, and as a coach, that is all you can ask your players to do when you are in that sort of situation.
"The big thing about when you lose is that it's painful, isn't it? It sharpens the mind, it sharpens the attitude, and you look at things probably a little deeper than you normally do.
"We try to learn when we win, but in this case we had a side that beat us because on the day they were a little better than us. We have to acknowledge that and then go 'OK, how can we be better than them?' And we will do that through the week, do our best to stay 15 on 15 and then see if we can get some strategies going.
"Everyone will be excited next week. It will be great. Rugby has been needing something like this for a while. It's now got it, so everyone will be a bit nervy about that because it could go either way, and how exciting is that?
"It's moments like this series that go down in history and excite young people to say 'hey, I want to be part of this', not only as a player, but also as a fan.
"It wasn't great conditions for watching last night [Saturday], but who cares that it was raining last night. You ask any of those Lions fans whether they felt the rain, I bet you they didn't. Did ours? I don't think they would have either."
New Zealand's next fixture after the Lions decider is a Rugby Championship clash against Australia on August 19.
After the hearing, Williams gave his reaction, which was posted in a series of tweets published on the All Blacks' official Twitter account.
Williams, 31, said he was "really disappointed, but happy with being able to get in there and say my piece".
He added: "They've come to the conclusion that it was reckless, it wasn't intentional.
"I've got in contact with Anthony, and I've apologised to him."
And in a final tweet, Williams added: "...but very disappointed that I was sent from the field last night and let my brothers down."