WEST Coast defender Ashton Hill will miss the rest of the season after scans confirmed she tore her ACL while trying to avoid an opponent in the loss to Collingwood.
Fremantle midfielder Stephanie Cain tore the ACL in her left knee on the same day during the opening minutes of her team's win over Geelong.
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St Kilda confirmed on Monday that Nadia von Bertouch had also ruptured her ACL on Sunday.
Von Bertouch suffered the injury during the third quarter of the loss to Western Bulldogs, but managed to play out the game.
Fremantle's AFLW high performance manager Kate Starre said Cain will undergo surgery in the coming week.
"It's heartbreaking to have an injury to that extent and to have another ACL," Starre said.
"We'll go through the rehab process and get her up and about as soon as we can.
"We've seen with the ACL injuries that we've had so far that the girls have all responded so well to their rehab programs.
"Steph will be no different, she'll be up and about as soon as possible."
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West Coast's head of female football Adam Selwood said the club would do whatever it takes to help Hill recover and get back out on the field in 2021.
"It's absolutely devastating for Ashton and the club," Selwood said.
"We know how hard she has worked to get to this point to become a really well-prepared and consistent performer at AFLW level."
Selwood also confirmed that defender Brianna Green would be unavailable indefinitely as she works her way back from general soreness.
Fremantle will start as hot favourites when they take on West Coast in the first ever AFLW western derby on Saturday.
A crowd in excess of 30,000 is expected to attend the match at Optus Stadium.