World Rugby has published the ranking permutations for the November internationals in Europe and North America and matches in the Rugby Europe Men's Trophy and Conference this weekend.
South Africa’s position at the top of the rankings is safe for at least another week if they beat Japan, even though they can’t improve their rating with a win.
The points differential between the Springboks and Japan is too big, at 18.95 points, for a victory to be rewarded.
Neither the All Blacks nor Ireland, who meet in Chicago, can better their rating of 92.20 points in victory, unless the Brave Blossoms can repeat the Miracle of Brighton, or hold the Springboks to a draw.
The best that Ireland can achieve is 91.36 points, while the All Blacks will move on to 91.49 points if they prevail by more than 15 points.
If South Africa is held to a draw at Wembley Stadium, the winning margin in the Chicago game would have to be more than 15 points for either team to move to number one.
A beaten South Africa will lose their number one ranking to the winning team in Chicago, irrespective of the scoreline.
A draw for Japan would move them into the second band of teams for the Men’s Rugby World Cup 2027 Draw, with Wales dropping out of the top 12 and replacing the Brave Blossoms in 13th.
Japan will climb an additional place, to 11th, in victory with Georgia, the team to fall as a result of the outcome at Wembley.
Ireland will replace the All Blacks in second place if they repeat their 2016 victory over them in Chicago.
With fourth-ranked France not in action and unable to improve its rating, New Zealand cannot fall lower than third with a defeat this weekend.
Australia will enter the top six, and the Band 1 positions come Draw time, if they avoid defeat against England, climbing above Argentina into sixth in the event of a draw.
A win by more than 15 points will also lift the Wallabies above England into fifth.
England will move up to fourth at France’s expense if they beat Australia, who will hang onto seventh place even if they are well beaten at Allianz Stadium.
This is because Scotland, their nearest rivals, will not be rewarded for beating the USA, given they have home advantage and are 14.17 points better off than the Men’s Eagles.
Scotland will drop below Fiji if they fail to win, while a first-ever victory at Murrayfield for the USA will see them leapfrog Spain into 14th.