Britain's Emma Raducanu says it is a "great gift" to play 23-time Grand Slam singles champion Serena Williams for the first time in her career.
The pair will play at 00:00 BST on Wednesday when they meet in the Western and Southern Open first round.
Earlier this week, 40-year-old Williams suggested she would soon retire from tennis, saying she will be "evolving away" from the sport after the US Open.
Raducanu, 19, is preparing to defend her US Open title later this month.
"I think it's going to be an exciting match," said Raducanu, whose first memory of seeing Williams play was when she went to Wimbledon as a seven-year-old.
"It's an amazing opportunity to play probably the best tennis player of all time. It's probably going to be my last opportunity to ever play her.
"I think that, for our careers to have crossed over, I think I'm really fortunate that I get to play her. Whatever happens, I think it's going to be a really good experience for me and something that I will remember for the rest of my life.
"It's a great gift to play the best on her way out from the sport."
The British number one won the Flushing Meadows tournament last year as an unseeded 18-year-old, 22 years after Williams won her first Grand Slam singles title in New York, aged just 17.
The pair were due to play on Monday, but the match was pushed back to Tuesday's night session in Cincinnati after rain delayed Sunday's play.
The winner will face either Victoria Azarenka or Kaia Kanepi in the second round.