Naomi Osaka has revealed she gets "really nervous" when talking to her idol Serena Williams.

The four-time Grand Slam winner discussed Williams’s impending retirement, with the sporting legend announcing earlier this month that she would be “evolving away from tennis”.

It is expected that Williams will hang up her tennis racquet after the US Open, which is set to get underway tomorrow.

"I watched her first match in Toronto before she announced it," Osaka told reporters. "For some reason I just started crying because I felt it.

"Then she announced it the day later. I'm like, 'Oh, my God, this is what devastation must feel like.' It really is an honour just to keep watching her play."

Osaka and Williams have played five times, with the Japanese star triumphing on three occasions.

Despite the familiarity with Williams on the court, Osaka admitted she still got tongue-tied around her idol off the court.

"I just get really nervous around her," she said. "It's really weird to idolise someone, then boom, you're just talking to them. I don't know. I feel stressed out. But she's really sweet. She's given me pointers sometimes.

"I know she didn't call it a retirement, she called it an evolution, which I think is really cool.

“I feel like the term 'retirement' kind of means an end to something. But since she says 'evolution,' it means a continuing journey."

Williams will play Danka Kovinić in the first round of the US Open, while Osaka, who has endured an injury-plagued season, will meet Danielle Collins.

“I feel like I would have lied a day ago or so and said that I was really relaxed," Osaka said. "But actually when I practiced today I felt very anxious.

“I think it's because I really want to do well because I feel I haven't been doing well lately.

"I don't know. It's tough. Of course, you don't want to lose in the first round of a Slam. I feel like I always do pretty well here. It's kind of taking the pressure off of myself, but it's always going to be there."

Iga Świątek, Simona Halep and Coco Gauff are among the favourites to win the US Open, while Emma Raducanu is set to defend her title at Flushing Meadows.