Rafael Nadal is tantalisingly close to securing the year-end world number one for a fourth time at the Paris Masters after Roger Federer's decision to withdraw from the final Masters Series 1000 event of the season.
The 36-year-old won his eighth title of the year at the Swiss Indoors in Basel, beating Juan Martin del Potro in three sets in the final to move to 96 singles title.
But to ensure he is full fit for the ATP World Tour Finals in London in November, Federer has opted to skip Paris. While the decision confirms his participation in the season-ending tour finals it all but ends his bid to finish 2017 as the world number one.
Federer trails Nadal by 1,470 points in the rankings and though 1,500 are available in the English capital, the Spaniard can secure the year-ending number one if he wins his first match in Paris where he resumes his campaign after knee soreness.
Nadal can claim the 45 points he needs to hold off Federer if he beats Hyeon Chung in the second round on Tuesday (31 October) after the South Korean player defeated Mischa Zverev. He won their only previous meeting on clay in Barcelona in April.
Even if Nadal is upset by Chung he will have another chance to remain world number one at the turn of the year if he wins any of his three group matches at the ATP World Tour Finals, where 200 ranking points are on offer for each victory.
In the event Nadal crashes out in the second round in Paris and loses all three of his group matches at the O2 Arena then Federer could potentially finish the year at the summit of men's tennis but only if he ends the season-ending tour finals as the undefeated champion.
Just two berths are yet to be filled in London heading into the concluding ATP event of the regular season. David Goffin can join Nadal, Federer, Alexander Zverev, Dominic Thiem, Marin Cilic and Grigor Dimitrov if he reaches the Paris semi-finals. He begins his campaign against either Adrian Mannarino or David Ferrer having been given a first round bye.
The final spot could feasibly be filled by handful of players. Pablo Carreno Busta is the current incumbent but the likes of Sam Querrey, Kevin Anderson, Juan Martin del Potro, Jo-Wilfried Tsonga and Lucas Pouille will all leapfrog the Spaniard if they win the title this week.