Stan Wawrinka injured his lower back to hand Roger Federer a walkover to the semi-finals in Basel
Stan Wawrinka set up a quarter-final clash with fellow home favourite Roger Federer at the Swiss Indoors Basel before having to pull-out of the contest immediately due to injury.
Wawrinka, the seventh seed, triumphed 6-3 3-6 7-5 against American Frances Tiafoe on Thursday in a match that lasted just over two-and-a-half-hours.
Top seed and defending champion Federer is looking to win the tournament for a 10th time. He will take on the winner of the meeting between third-seeded Stefanos Tsitsipas or Filip Krajinovic on Saturday.