Chelsea announced on January 7 that striker Sam Kerr had suffered an anterior cruciate ligament injury.
The Australia star was hurt during a warm-weather training camp with her club side in Morocco.
"Sam will be assessed by a specialist in the coming days and then begin her rehabilitation with the club's medical team," the Women's Super League champions said in a statement.
"Everyone at Chelsea would like to wish Sam the very best for her recovery."
Matildas coach Tony Gustavsson said: "Considering how hard Sam has worked over the past six months to return to play, this news is a devastating blow for everyone.
"With her ability to lead by example, Sam's guidance and influence on the team is significant and, as a result, this will be an incredible loss for the national team.
"Our focus now is on ensuring she has all the support she wants and needs to navigate recovery and rehab."
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Sam Kerr ACL injury: What happened to Chelsea striker?
Chelsea confirmed on January 7 that Kerr had sustained ACL damage during a warm-weather training camp in Morocco. It was not initially clear how the injury had occurred.
Emma Hayes' side have not played since December 20, when Kerr scored the opening goal in a 3-1 win away to Hacken in the UEFA Women's Champions League.
Chelsea's next match is on January 14, when they host West Ham in the Fourth Round of the FA Women's Cup.
When will Sam Kerr be back from injury?
It is not yet clear how long Kerr will be sidelined. Chelsea stressed that the 30-year-old would need assessment from specialists before her rehabilitation work could begin.
Generally, the recovery period for a serious ACL injury, such as a partial or complete tear of the ligament, between six and nine months. That would mean Kerr is likely to be unavailable until at least July 2023.
What games will Sam Kerr miss?
Kerr will now sit out the rest of the 2023/24 Women's Super League season, as well as the UEFA Women's Champions League.
She will also miss the AFC Women's Olympic Qualifiers Round3 series against Uzbekistan, which takes place across two legs in late February.
Chelsea have another 12 Super League matches in 2023/24, culminating in a clash with Manchester United on May 18.
They have two more group games in the Women's Champions League, in which they are expected to reach the quarterfinal stage, which takes place in March.
Will Sam Kerr play at the 2024 Olympics?
Australia are in the third round of the AFC Women's Olympic Qualifying Tournament. They will face Uzbekistan in a two-legged tie in February.
The winner of that matchup, along with the winner of the other tie between North Korea and Japan, will qualify for the 2024 Olympic Games in Paris.
The Games begin on July 26, 2024, so it looks highly unlikely that Kerr will be available to play at the tournament if the Matildas qualify. However, she cannot be definitively ruled out until she completes the specialist assessment of her knee injury, at which point a more precise recovery time will be known.
