The Briton was due to face Coco Gauff in the last 16.
Johanna Konta’s frustrating summer appears to have taken another turn for the worse after she withdrew from the National Bank Open in Montreal
The British number one was due to face American 15th seed Coco Gauff for a place in the quarter-finals on Thursday but pulled out due to a knee injury.
Konta had been hoping for a prolonged run at the WTA Tour event after missing both Wimbledon and the Olympics.
The 30-year-old was unable to play at the All England Club after being deemed a close contact of someone who had tested positive for Covid-19. She then contracted coronavirus herself and was unable to travel to Tokyo.
Her return to action in Canada had been going well and she reached the third round by battling back from a set down to beat third seed Elina Svitolina on Wednesday.
A tweet from the WTA Tour read: “Johanna Konta has withdrawn from Montreal due to a left knee injury. Coco Gauff advances to the quarter-finals via walkover, will face either (Petra) Kvitova or (Camila) Giorgi.”