US Open champion Bianca Andreescu has withdrawn from the Australian Open in Melbourne as she continues her recovery from a knee injury.

The Canadian, ranked sixth in the world, picked up the injury at the season-ending WTA Finals in October.

Andreescu beat Serena Williams at Flushing Meadows in September to win her maiden Grand Slam title.

"I have to respect the recuperation plan for my knee and body," the 19-year-old wrote on Twitter.

"I feel better and stronger every day but the Australian Open is unfortunately too soon in my rehab process."

Andreescu reached the second round in Melbourne in 2019.

Another absentee from the Australian Open will be Argentine Juan Martin Del Potro, 31.

The 2009 US Open winner has been battling problems with his right knee since June last year when he had surgery.

Del Potro, twice a Melbourne quarter-finalist, was ranked in the top 10 a year ago, but has fallen to 120 in the singles rankings after six months out of action.