The last time the Serb had led the ATP rankings was on October 31, 2016.
Roger Federer had cast doubts in his appearance in Paris this season, after competing and triumphing in Basel just a few days back. At the US Open, he retired during his match against Juan Martin del Potro.
"Yesterday, in the long match with Jo, in the middle of the second set, I overextended my elbow and it did some kind of pain", Raonic said. It would not be fair and not good for me and for nobody to go inside the court knowing that probably the full tournament will not be possible to play'.
The Swiss world number three will play the victor of the tie between France's Jo-Wilfried Tsonga and Croatia's Milos Raonic on Wednesday after receiving a bye in the first round.
Thai billionaire's family visit Leicester crash site
May said her thoughts were with the family and friends of the victims as well as supporters of the club. The helicopter went down after clearing King Power Stadium at 20:30 BST.
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 Swiss star missed the event the past two years due to a combination of injury and selective scheduling. He then skipped the Asia swing to recover, missing tournaments in Beijing and Shanghai. "And I have also not played in this city for some time", said the Basel open champion.
Federer, who won his 99th career title at the Swiss Indoors last Sunday, will face 13th-seeded Fabio Fognini.
'As you know, when you come back after injuries, and you push a little bit the body at the beginning, some issues can happen'.
In the early action on Wednesday, Kei Nishikori and John Isner kept their hopes of gatecrashing the Tour Finals alive with victories.
The 16th-seeded Sock saved all four break points he faced in a 6-3, 6-3 win against Frenchman Richard Gasquet, while Zverev advanced 6-4, 6-4 over American Francis Tiafoe.