The tennis star made the comment as First Lady Michelle Obama was confirmed as the latest big name to tape a Carpool Karaoke segment with James Corden.
Corden hosts US talk series The Late Late Show and Carpool Karaoke, which features the 37-year-old entertainer singing in a car with celebrities, has welcomed A-listers including Tom Hanks, One Direction and David Beckham.
The highlight of Baseline Sessions’ glittering evening, attended by the likes of model Daisy Lowe and designer Sadie Frost, will be Williams performing karaoke.
Asked about the First Lady’s vocal skills compared with her own, Williams admitted that singing is not her forte.
“I’m not the world’s greatest singer so I’m not sure I’ll give her a run for her money,” she told the Press Association.
“But that’s really cool that she’s doing Carpool Karaoke.”
Williams, who has been an ambassador for Delta Air Lines since 2013, has long been a fan of karaoke.
In 2015, she performed Disney classic Under The Sea from The Little Mermaid at Delta’s Open Mic Night in New York City.
The year before, she treated fans to a rendition of Diamonds Are A Girl’s Best Friend, the song made famous by Marilyn Monroe.
The world number one also surprised many by dancing in the new video for Beyonce’s single Sorry.
However, her main focus remains tennis.
Williams, the reigning Wimbledon champion, is still one Grand Slam victory away from equalling Steffi Graf’s haul of 22 Grand Slam wins.
“My form is really good,” she said in response to a question about her hopes for Wimbledon, which starts on Monday.
“I feel I’m playing well. I’m happy to be here and I love playing on the grass.”
She is also proud to be a role model for women and people from an ethnic minority background.
“I embrace it, I really do. I love it,” she said.
Celebrity guests at Baseline Sessions With Serena Williams lined up to hail the sports star’s athleticism and achievements.
TV presenter Donna Air, currently a contestant on BBC One’s Celebrity MasterChef, said: “She’s fantastic. She’s like a machine.”
Croatian tennis player Marin Cilic said Williams “stands at the top” due to her many wins, which include doubles and mixed doubles titles.
He added: “She can still make an impact … Wimbledon is her favourite.”
Fashion designer Frost, 51, applauded Williams’s “strong character”.
Model Lowe, 27, also paid tribute to the American who arrived on the tennis scene alongside her sister Venus Williams in the late 1990s.
“I hope she wins Wimbledon,” Lowe enthused. “She’s so fantastic. Incredible!”
Williams, who was dressed in white trousers and a white top for Wednesday night’s festivities, also said she has a list of favourite karaoke songs.