• Raducanu has suffered a series of injuries since then and is currently sidelined after wrist and hand surgery.
• Raducanu split with coach Sebastian Sachs, her fifth coach in less than two years, in June.
Emma Raducanu said "sometimes I think to myself 'I wish I'd never won the US Open'" as she spoke about her physical and mental struggles since then.
The 20-year-old claimed a stunning 2021 US Open title when she became the first qualifier to win the Grand Slam.
Raducanu has suffered a series of injuries since then and is currently sidelined after wrist and hand surgery.
"I was struggling with the physical pain but the mental side of it was really difficult for me too," she said.
Speaking to The Times,the Briton added: "I always want to put forward the best version of myself, or strive for that, but I knew I couldn't."
Raducanu split with coach Sebastian Sachs, her fifth coach in less than two years, in June.
She has played only 10 WTA Tour matches in 2023, winning just five, with three of those victories coming at Indian Wells.
"I very much attach my self-worth to my achievements," she said.
"If I lost a match I would be really down, I would have a day of mourning, literally staring at the wall. I feel things so passionately and intensely."
Raducanu did not drop a set on the way to victory at the US Open in New York when she beat Leylah Fernandez 6-4 6-3 in the final.
But she has not gone beyond the second round of a Grand Slam since then and her ranking has tumbled from 10th in July 2022 to 128th.
She missed this year's French Open and will also be absent from Wimbledon after minor operations on her ankle and hands.
"That moment on the court, when I was celebrating [the US Open win], I was like, I would literally trade any struggle in the world for this moment," said Raducanu.
"Anything can come my way, I will take it for what I have right now because this is the best thing in the world. I promised myself that, on the court that day.
"Since then I've had a lot of setbacks, one after the other. I am resilient, my tolerance is high, but it's not easy. And sometimes I think to myself 'I wish I'd never won the US Open, I wish that didn't happen'.
"Then I am like, 'remember that feeling, remember that promise', because it was completely pure."
Raducanu,who signed a number of commercial deals after her US Open victory, said she has "had to mature very quickly" since her rise to fame as she had been "extremely naive".
"What I have realised in the past two years, the tour and everything that comes with it, it's not a very nice, trusting and safe space," she added.
"You have to be on guard because there are a lot of sharks out there. I think people in the industry, especially with me because I was 19, now 20, they see me as a piggy bank.
"It has been difficult to navigate. I have been burned a few times. I have learned, keep your circle as small as possible."