- Second seed Andy Murray withdraws from Swiss Indoors event with buttock strain
- Defending champion Roger Federer moves into last eight, beating Jarkko Nieminen
- Federer was in same half of draw as Murray and they could have met in semifinals
- Valencia Open titleholder David Ferrer moves into last eight of Spanish event
Roger Federer's hopes of a Swiss Indoors final rematch with Novak Djokovic were boosted when Andy Murray withdrew from the tournament on Wednesday.
The British player moved above Federer into third place in the world rankings after winning three tournaments in Asia, but was unable to face Dutchman Robin Haase in his opening match in Basel due to a strained buttock muscle.
"I woke up yesterday and was really struggling to walk," second seed Murray, who accepted a late wildcard entry, told the ATP Tour website.
"I went to a swimming pool nearby and did some exercises and it felt a little better, but I was forced to cancel my practice yesterday. It is just a freak thing and I have no idea how I did it."
Federer, who was drawn to meet Murray in the semifinals, moved into the last eight with a battling 6-1 4-6 6-3 win over Finland's Jarkko Nieminen in his second-round match on Wednesday. It was his 12th straight win against his fellow 30-year-old, but his first not in straight sets.
A record four-time winner of his home event, Federer -- like world No. 1 Djokovic -- had taken six weeks off after the U.S. Open.
The defending champion will next face either American seventh seed Andy Roddick or Radek Stepanek of the Czech Republic.
Marcus Baghdatis also earned a place in the quarterfinals, with the Cypriot overcoming Swiss player Michael Lammer 7-6 (7-2) 6-7 (2-7) 6-3 to set up a possible clash with Djokovic -- the 2009 winner and last year's runner-up.
Djokovic will play Lukasz Kubot in the second round after the Pole beat fellow qualifier Tobias Kamke 5-7 7-5 6-2 on Wednesday.
Sixth seed Janko Tipsarevic's hopes of qualifying for the season-ending ATP World Tour Finals were dented after the Serbian was forced to retire during his opening match against Florian Mayer, trailing the German 5-1.
Tipsarevic must now reach the final or even win next week's Paris Masters if he is to snatch the eighth and last place from Mardy Fish. The American also exited early after suffering a hamstring injury in his first-round match on Tuesday.
Mayer will next face Croatia's Ivan Ljubicic, with the winner of that second-round match to play Haase or Switzerland's Stanislas Wawrinka.
David Ferrer continued his Valencia Open title defense by reaching the quarterfinals with a 6-3 6-3 win over Canadian qualifier Vasek Pospisil on Wednesday.
The Spaniard will next play Russia's Nikolay Davydenko, who had a walkover when French qualifier Nicolas Mahut withdrew from their second-round tie for family reasons.
Third seed Gale Monfils also progressed into the last eight, beating Chile's Pablo Andujar 6-2 7-6 (7-5) to set up a clash with Canada's Milos Raonic or Spain's Marcus Granollers.
Argentine sixth seed Juan Martin del Potro won his first-round match, beating Russia's Dmitri Tursunov 6-4 6-1.
The 2009 U.S. Open champion next plays big-serving South African Kevin Anderson.