TORONTO -- Canadian tennis star Bianca Andreescu will take a mental break from tennis and sit out the start of next season, including the Australian Open, saying she wants to "re-set, recover, and grow" after a challenging two years that included getting COVID-19.

The 21-year-old from Mississauga, Ont., that she was affected mentally and physically by "multiple weeks in isolation quarantining" and that her grandmother's stay for several weeks in a hospital's intensive care unit because of the coronavirus "really hit me hard."

"A lot of days, I did not feel like myself, especially while I was training and/or playing matches. I felt like I was carrying the world on my shoulders," said the 2019 U.S. Open champion. "I could not detach myself from everything that was going on off the court; was feeling the collective sadness and turmoil around and it took its toll on me."

Andreescu joins other professional athletes who have cited the need for time away from competition to gather themselves mentally -- including, for example, Naomi Osaka, a four-time major title winner and former No. 1-ranked player in tennis. Osaka took a break after pulling out of the French Open in May and again after her loss at the U.S. Open in September, sitting out the remainder of the season.

Andreescu was 19 when she capped a breakthrough season by upsetting her idol, Serena Williams, in the U.S. Open final two years ago. Soon after, Andreescu rose to a career-best No. 4 in the WTA rankings.

But in October 2019, she tore the meniscus in her left knee and was gone from the tour for about 15 months.

Andreescu returned to action at this year's Australian Open, where Williams offered this assessment: "She has a bright future. She's really young; rather incredibly mature. I've always said I think her light burns brightly. She really has a great game to continue to win more Grand Slams."

Andreescu won her opening match in Melbourne, then lost in the second round. She wound up going 4-4 in Grand Slam tournaments in 2021, including a fourth-round run at the U.S. Open and first-round exits at the French Open and Wimbledon.

That was part of an overall 17-12 mark on tour with no titles this season, leaving her ranking at No. 46 entering 2022.

She said in April that she had tested positive for COVID-19. In June, she announced that she would no longer be coached by Sylvain Bruneau after four years together.

What Andreescu left unclear Monday was when she will be back on court.

"I want to give myself extra time to re-set, recover, and grow from this (as cliche as that sounds) and continue to inspire by doing charity work, giving back and working on myself because I know by doing this, I will come back stronger than ever," she wrote. "I will therefore not start my season in Australia this year, but will take some additional time to reflect, train, and be ready for the upcoming 2022 tennis season."