Quebec City - Canada's Aleksandra Wozniak injured her right shoulder during a warm-up session and withdrew from Bell Challenge on Thursday before her scheduled second-round match against Melanie Oudin.
Wozniak, ranked 48th, said she will have a scan on Friday morning.
In other second-round matches, Anna Tatishvili beat seventh-seeded Petra Martic 6-2, 6-3, and Kirsten Flipkens edged Mirjana Lucic 6-7 (2), 6-2, 6-4.