Scans have confirmed that St Kilda's Ben Paton will miss the 2021 season, following fractures to his fibula and tibia bones on Thursday.
The young defender was assisted from the track following the incident during match simulation at training.
"This is a devastating result for Ben," St Kilda chief operating officer Simon Lethlean said.
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"He had such a strong year last year and had continued that form throughout the pre-season.
"We know Ben will quickly turn his mind to rehab and how to get back out on the field as soon as possible, and he'll have our full support to do so."
Paton was caught in a tackle by staff member Jarryd Roughead when the break occurred, who was a fill in during the intraclub match with a host of Saints players already on the sidelines.