Rafael Nadal will be crowned as the year-end world No 1 if he wins his first showdown at this week’s Paris Masters, after Roger Federer withdrew from the tournament.
The two old rivals have both had stunning seasons, returning to form and fitness with two grand slam titles each.
But Federer, 36, who could have still usurped Nadal, 31, at the top of the rankings with titles in the French capital and at the World Tour Finals in London, pulled out of the final event of the regular season to protect a back problem.
Federer said winning his eighth Swiss Indoors title on Sunday – against Juan Martin del Potro – had left him unfit to play at the Bercy Arena.
“I am very sorry to have to pull out of the Paris Masters, but my body needs a rest after Basel,” the Swiss legend said.
“I’ve played a lot of tennis this year and need to make sure I look after my physical wellbeing if I want to continue to compete at the highest level for years to come. “I’d like to be fully fit for London and for 2018.” Top seed Nadal, who has a bye for the first round in Paris, just needs to win his opening second-round clash to secure the top ranking heading into next year.
The Spaniard, who claimed his 10th French Open title and the US Open crown to take his grand slam tally to 16 major titles this season, will start his campaign against either German serve-and-volleyer Mischa Zverev or promising South Korean Hyeon-chung.
Despite his love of the clay of Roland Garros, Nadal has never won the Paris Masters in five previous attempts at the indoor tournament.
Nadal’s best effort came with a final defeat by David Nalbandian in 2007.
The Bercy hard courts will also see the final two places for the World Tour Finals decided, with seven players still hunting a London ticket.
Belgian David Goffin and US Open semifinalist Pablo Carreno Busta hold the seventh and eighth spots at present.
But Sam Querrey, South African Kevin Anderson, Del Potro, Jo-Wilfried Tsonga and Lucas Pouille all remain in contention.
Former US Open champion Del Potro, 29, has made a stunning late charge after being 47th in the points standings only two months ago.
He reached the semis at Flushing Meadows, beating Federer on the way, before also making the Shanghai Masters last four and winning in Stockholm ahead of his runner-up effort in Basel.
That makes the Argentine the form man going into Paris, where he will play either Italian Paolo Lorenzi or qualifier Joao Sousa in round two.
Frenchman Pouille is also making a bid.