Scotsman Andy Murray will take over from Novak Djokovic as world number one when the rankings are updated on Monday after his Paris Masters semi-final opponent Milos Raonic pulled out through injury on Saturday.
“Yesterday at I believe 4-2 in the first set I started feeling some pain in my leg,” fourth-seeded Canadian Raonic told a news conference, referring to his match with Frenchman Jo-Wilfried Tsonga.
“I didn’t think too much of it at that point. I had an MRI half an hour ago… they found that I have a grade one tear in the right quadriceps.”
Murray was guaranteed to climb from second to first in the rankings if he reached the final.
Serb Djokovic, who has been number one since July 2014, was knocked out in the quarter-finals by ninth seed Marin Cilic on Friday.
The Croat was then beaten 6-4 6-3 in the semi-finals on Saturday by American John Isner.