Canada's Bianca Andreescu has dropped out of the Australian Open tennis tournament because of a lingering left knee injury.

The reigning U.S. Open champion and Canada's first winner of a Grand Slam singles tournament hasn't played since suffering the injury at the WTA Finals in October in China.

"The Australian Open is unfortunately too soon in my rehab process and I sadly will not be able to play in it this year," Andreescu, a 19-year-old from Mississauga, Ont., tweeted.

"It was a very tough decision to make as I love to play in Melbourne but I have to respect the recuperation plan for my knee and body."

The Australian Open, the first Grand Slam of the season, starts Jan. 20.

Ranked sixth in the world after starting 2019 outside the top 150, Andreescu has been bothered by injuries while making her climb.

No Canadian women in main draw

A shoulder injury last March kept her out of all but one match from April through July.

Andreescu retired after one match at last year's French Open and didn't play at Wimbledon in 2019.

The Canadian returned to win the Rogers Cup in Toronto before capturing the U.S. Open in New York. At one point last year, Andreescu won 17 matches in a row.

Hey guys, just wanted to give you a little update on my knee rehab after I got injured at the WTA finals in Shenzhen. My rehab is going well, I feel better and stronger every day but after discussing it with my team and following the recommendation of the doctors, the Australian —@Bandreescu_ Open is unfortunately too soon in my rehab process and I sadly will not be able to play in it this year. It was a very tough decision to make as I love to play in Melbourne but I have to respect the recuperation plan for my knee and body. I can’t wait to come back to Aus soon x —@Bandreescu_

Andreescu's decision leaves Canada without a woman in the Australian Open's main draw.

Eugenie Bouchard of Westmount, Que., and Leylah Annie Fernandez of Laval, Que., are entered in qualifying next week.

Canada has four players in the men's main draw — Denis Shapovalov of Richmond Hill, Ont., Montreal's Felix Auger-Aliassime, Milos Raonic of Thornhill, Ont., and Vancouver's Vasek Pospsil.

Australian Open organizers also announced Saturday Argentina's Juan Marin del Potro and Richard Gasquet of France have withdrawn due to knee injuries.