Bianca Andreescu (C front) of Canada consoles Serena Williams of the United States after the women's singles final at the in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Serena Williams of the United States serves against Bianca Andreescu of Canada during the women's singles final at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada returns the ball against Serena Williams of the United States during the women's singles final at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu (2nd R) of Canada hugs Serena Williams of the United States during the awarding ceremony of the women's singles event at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada celebrates victory with trophy during the awarding ceremony of the women's singles event at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada returns the ball against Serena Williams of the United States during the women's singles final at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Serena Williams of the United States wipes tears during the awarding ceremony of the women's singles event at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Serena Williams (2nd R, front) of the United States gets medical treatment during the women's singles final at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Serena Williams of the United States returns the ball against Bianca Andreescu of Canada during the women's singles final at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada poses for photos with trophy during the awarding ceremony of the women's singles event at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada celebrates victory with trophy during the awarding ceremony of the women's singles event at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada poses for photos with trophy during the awarding ceremony of the women's singles event at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)

Bianca Andreescu of Canada returns the ball against Serena Williams of the United States during the women's singles final at the 2019 Rogers Cup in Toronto, Canada, Aug. 11, 2019. Serena Williams of the United States retired due to injury and Bianca Andreescu of Canada claimed the title. (Xinhua/Zou Zheng)