Briton Andy Murray will take over from Novak Djokovic as World No 1 when the rankings are updated on Monday after his Paris Masters semi-final opponent Milos Raonic withdrew with a leg injury on Saturday.
"I have a tear in my right quad," Canadian Raonic told a news conference.
Briton 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, who was guaranteed to climb from second to first in the rankings if he reached the final, is the first Briton to get to number one.
At 29 years and 174 days, he will be the oldest player to reach the summit for the first time since John Newcombe in 1974.
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.
Raonic is now doubtful for the season-ending ATP World Tour Finals to be held in London from November 13-20.
"I still have the possibility of making it but I was told five to 10 days so I'm on the borderline," he said.
Factbox: Previous ATP world number ones
Chronological list of former ATP world number ones since computer rankings were introduced in 1973.
Year first achieved and total weeks spent at number one in brackets.
Ilie Nastase (Romania) - (1973, 40 weeks)
John Newcombe (Australia) - (1974, 8)
Jimmy Connors (US) (1974, 268)
Bjorn Borg (Sweden) - (1977, 109)
John McEnroe (US) - (1980, 170)
Ivan Lendl (CzechRepublic) - (1983, 270)
Mats Wilander (Sweden) - (1988, 20)
Stefan Edberg (Sweden) - (1990, 72)
Boris Becker (Germany) - (1991, 12)
Jim Courier (US) - (1992, 58)
Pete Sampras (US) - (1993, 286)
Andre Agassi (US) - (1995, 101)
Thomas Muster (Austria) - (1996, 6)
Marcelo Rios (Chile) - (1998, 6)
Carlos Moya (Spain) - (1999, 2)
Yevgeny Kafelnikov (Russia) - (1999, 6)
Pat Rafter (Australia) - (1999, 1)
Marat Safin (Russia) - (2000, 9)
Gustavo Kuerten (Brazil) - (2000, 43)
Lleyton Hewitt (Australia) - (2001, 80)
Juan Carlos Ferrero (Spain) - (2003, 8)
Andy Roddick (US) - (2003, 13)
Roger Federer (Switzerland) - (2004, 302)
Rafael Nadal (Spain) - (2008, 141)
Novak Djokovic (Serbia) - (2011, 223)
Andy Murray (Britain) - (2016, 1*)