Stan Wawrinka defeated the American Frances Tiafoe in a three-set quarter-final match on Thursday at the Basel's Swiss Indoors.
The 34-year-old Lausanne native then announced he will not be able to face Roger Federer due to a back injury. "I got injured during the last game of the match", said Wawrinka. "I am so sad for not competing here in Basel again this year. I am very sorry."