UNTRIED Melbourne defender Aaron Nietschke has ended his first full year at the club with a second anterior cruciate ligament injury.

Nietschke initially ruptured the ACL in his right knee in February, before re-injuring the same knee at last Friday's training session in a devastating blow for the 19-year-old.

He will almost certainly miss the entire season – meaning his two-year deal would expire without him playing a game – but the Demons have already told him they will offer him a new contract. 

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Melbourne football boss Josh Mahoney confirmed Nietschke's bad fortune on the club's website.

"Unfortunately, scans have confirmed that Aaron has ruptured his ACL graft, which will likely sideline him for the 2020 season," Mahoney said. 

"This is obviously incredibly disappointing news for Aaron and the whole team. He had really attacked his rehab and was in great shape prior to this incident. 

"He's a good young character who has shown a lot of resilience during his first year at the club and we have no doubt he will get through this again, giving himself the best chance to be available for our AFL team." 

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Nietschke, originally from South Australia, was the No.53 pick in last year's NAB AFL Draft.