The "countdown has begun" to Williams' retirement, the 23-time Grand Slam winner said this week. The 40-year-old is anticipated to say goodbye following a final major campaign at the US Open beginning later this month.
Williams overcame Spain's Nuria Parrizas Diaz in the first round at Toronto last week, winning her first singles match in more than a year.
That was before she said that she was "growing away" from tennis in a Vogue piece and on Instagram.
Belinda Bencic of Switzerland, who won the gold medal at the Tokyo Olympics, defeated Williams in straight sets in the second round in her first match following the news.
In Cincinnati, where she has won two championships, Williams will face yet another difficult journey.
The winner of Williams-Raducanu will take on either Victoria Azarenka, who is ranked 20th, or Kaia Kanepi of Estonia, who is ranked 31st.
The 33-year-old former world number one and two-time Grand Slam champion Azarenka was unable to compete in the Toronto tournament due to a visa issue.
The 19-year-old Briton Raducanu, who shot to fame with her run to the US Open triumph last year as a qualifier, has never faced Williams, who was 17 when she won the US Open in 1999 for her maiden major championship.
Since then, Raducanu has struggled to find momentum, exiting early at the Australian Open, French Open and Wimbledon.
Speaking about Williams in the wake of the American’s announcement of her retirement plans last week, Raducanu said Williams had “changed the game.”
“To dominate that much, there has not really been someone who has dominated like her in the women’s game.”
She also marvelled at how long Williams has remained a force in the sport from her first Grand Slam title to her most recent at the 2017 Australian Open, which was followed by trips to the US Open and Wimbledon finals in 2018 and 2019.
“That longevity of a career is something that a lot of the players, me especially, aspire to achieve,” Raducanu said.