Sam Naismith's knee is looked at by a trainer, and (inset) leaving the ground at the SCG in R4, 2020

SYDNEY ruckman Sam Naismith is set to miss the rest of the season after scans confirmed he ruptured the ACL in his right knee on Thursday night. 

Naismith, playing just his 30th AFL match, finished the loss to the Western Bulldogs on the bench with a knee injury sustained in the final term. 

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Sydney's head of football, Charlie Gardiner, said the club would continue to support Naismith, who has managed just two senior games since suffering his first ACL injury ahead of the 2018 season.  

Swans ruckman Sam Naismith. Picture: Getty Images/AFL Photos

"It is terrible news for Sam and really disappointing for the team," Gardiner said.

"He will see a surgeon next week and we will then lay out next steps from there.

"Our thoughts are with Sam at the moment and we will wrap our arms around him as he gets on with his recovery."

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Naismith underwent his first knee reconstruction in the pre-season of 2018 and sat out the rest of that season and then the entire 2019 campaign with further complications. 

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Swans coach John Longmire said on Thursday night that the injury was the latest in a series of difficult events for the 27-year-old. 

"He's missed two years of footy and comes back and plays round one and plays really well," Longmire said. 

"He lost his sister through that (shutdown) break and then he comes back and does his knee. It's a terrible run for him." 

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The Swans' ruck depth consists of Callum Sinclair (199cm) and Hayden McLean (197cm), both of whom played in the loss to the Dogs, plus rookie Michael Knoll (205cm) and Joel Amartey (197cm).