MELBOURNE has been dealt a major blow a month out from the NAB AFLW season, losing defenders Katherine Smith and Shae Sloane to ACL injuries in pre-season training.

Both will be forced to undergo surgery after sustaining injuries in separate sessions in recent weeks.

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Smith ruptured her ACL in an innocuous incident on Thursday, with scans also revealing she had suffered damage to her medial collateral ligament (MCL).

Sloane, the sister of Adelaide captain Rory, tore the ACL in her right knee in the Demons' last training session before Christmas – the same knee she ruptured in round one last season.

"It's obviously a devastating outcome for Shae and Katherine, who are both integral members of our team," Demons' AFLW football manager Daniel McPherson told the club's website.

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"While their injuries mean they won't be running out with their teammates this season, both girls will still play important roles in supporting the playing group over the next few months.

"We will obviously be doing everything we can to support both Shae and Katherine during this challenging time, as they begin their roads to recovery.

"They are both terrific characters, and we know their resilience and determination will ensure they push each other through their recovery and rehab to come back even stronger for the 2021 season."

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Demons ruck Lauren Pearce will miss the first month of the season after she was sent for an arthroscope in December on her troublesome knee.

Star midfielder Daisy Pearce is also on the comeback trail after the birth of twins Sylvie and Roy last February.

The Demons open their season against North Melbourne on February 8.