Novak Djokovic will return to the top of the ATP rankings following Rafael Nadal's withdrawal from the Paris Masters.
Nadal has pulled out of the final tournament of the regular season due to an abdominal injury, meaning the Serbian ends his two-year absence from the top of the pile when the new list is published on Monday.
Djokovic, who has won Wimbledon and the US Open in the last four months, was memorably disposed as world number one by Andy Murray in the French capital in 2016.
Nadal has not played since the US Open in September, when he suffered a knee injury in the semi-final and his comeback has been now been curtailed.
The Spaniard has not revealed whether he will play in next week's ATP Tour Finals in London.
He said in a press conference in Paris: "I arrived here a couple of days ago, as everyone knows I have been outside of the competition since the US Open.
"I took time off, I came back and it was great to be in Paris for a couple of days and practise with the guys.
"I enjoyed it, I feel, in terms of tennis, better than what I thought one week ago, but in the last few days I started to feel a little bit abdominal (pain), especially when serving. I checked with the doctor and the doctor recommended I did not play."
In the early action on Wednesday, Kei Nishikori and John Isner kept their hopes of gatecrashing the Tour Finals alive with victories.
Nishikori beat Frenchman Adrian Mannarino 7-5 6-4 while Isner battled past Mikhail Kukushkin
6-3 6-7 (2) 7-6 (1).
Fourth seed Alexander Zverev booked his place in the next round with a 6-4 6-4 win over Frances Tiafoe.