French Open champion and world No 4 Stan Wawrinka was forced to withdraw from the Metz ATP event Friday with an ankle injury, handing Philipp Kohlschreiber a semi-final spot.
Top seed Wawrinka had twisted his right ankle at the end of the first set of his second-round contest with Dustin Brown on Thursday.
"Unfortunately, I have to pull out because yesterday I twisted my ankle at 5-4 in the first set," said Swiss star Wawrinka.
"It was painful in the match, but still OK with tape on it. But after a lot of treatment last night and some tests this morning, it's dangerous for me to play because the pain is still there. So I will have to see a doctor to see if I will be OK in the next few weeks."
German fifth seed Kohlschreiber will face Jo-Wilfried Tsonga, who beat fellow Frenchman Nicolas Mahut 6-7 (6/8) 6-3 7-5 for a place in the final.
In the other quarter-finals on Friday, French second seed Gilles Simon beat Luxemburg's Gilles Muller 6-4 6-4 while Martin Klizan of Slovakia came from behind to defeat Spanish fourth seed Guillermo Garcia-Lopez 4-6 6-3 7-6 (7/4).
