St Kilda have suffered their second major injury in as many days with the Saints' AFL intra-club match stopped for 25 minutes as Ben Paton received medical assistance.
Defender Paton was carried off the ground on Thursday with fears he has broken his leg.
Later on Thursday, the Saints confirmed he had fractured his fibula and tibia bones and would miss the season.
"This is a devastating result for Ben," St Kilda chief operating officer Simon Lethlean said.
"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 adds to a concerning injury list at Moorabbin.
On Wednesday, key ruckman Rowan Marshall was diagnosed with a foot stress injury and will be out of action for at least a month.
The 25-year-old, who forms a dangerous ruck-forward partnership with veteran big man Paddy Ryder, is expected to return "early in the season".