British pair Elena Baltacha and Heather Watson fell at the final hurdle in qualification for the Rogers Cup.
Baltacha, who beat France's Aravane Rezai in her previous match, suffered a 7-6 (7-5) 6-3 defeat by Greta Arn to miss out on a place in the main draw.
After a prominsing start, world number 108 Watson was overhauled 2-6 6-3 6-2 by Slovenia's Polona Hercog in Toronto.
The 19-year-old took the opening set, but Hercog, who is 68 places above her in the rankings, came through to win.
Baltacha is ranked 11 places higher than Arn, but her latest defeat makes it four losses in four matches with the Hungarian.
Anne Keothavong, who separates number one Blatacha and number three Watson in the British rankings, lost to Sharon Fichman in the first qualifying round.
The defeats mean there will be no British representation at the event which features every one of the world's top 20 and was won last year by current world number one Caroline Wozniacki.
Serena Williams is also in the draw as she looks to climb up the world rankings, but Venus Williams has withdrawn because of illness.