Serena hasn't played since retiring in the opening set of her first round at Wimbledon due to an ankle injury.

Editor's Note: On Wednesday, Rafael Nadal disclosed he would miss Cincinnati

Fans in Toronto, Montréal and Cincinnati have patiently waited two years for their respective tennis events to return. Unfortunately, the timing hasn’t aligned to see a crop of their sport’s biggest stars in person.

In Canada, names such as Novak Djokovic, Roger Federer, Ashleigh Barty, Naomi Osaka, Iga Swiatek and Dominic Thiem were MIA before the National Bank Open began. Rafael Nadal joined the list Tuesday when he withdrew ahead of his second-round match, deciding his left foot had not progressed enough to play a second straight week.

Not long after Nadal’s news, officials with the Western & Southern Open revealed their latest withdrawals. Two-time champion Serena Williams (leg), fellow former world No. 1 Venus Williams (undisclosed) and current U.S. No. 1 Sofia Kenin (foot) have all pulled out. Djokovic, Federer and Thiem, plus Stan Wawrinka, previously announced they would not be able to compete.

“I am still in recovery from my leg injury at Wimbledon," Serena said in a statement. "I will miss all of my fans in Cincinnati whom I look forward to seeing every summer. I plan to be back on the court very soon."

Added Kenin, "I am rehabbing well in hopes to play the US Open later this month. I feel another week of recovery is necessary."

Barty, Osaka and Swiatek remain entered at the event staged in nearby Mason, Ohio, while Nadal was unclear about his odds of participating next week. “Probably in the next couple of days, we're gonna know more,” he said.

Jenson Brooksby, Brandon Nakashima, Bernada Pera, Samantha Stosur, Jil Teichmann and Frances Tiafoe were named main draw wild card recipients.

Last year, Victoria Azarenka and Djokovic captured the titles when the tournament was held at the USTA Billie Jean King National Tennis Center. Needless to say, there are a mountain of question marks to ponder as we approach the final major of the year in New York.