The Sydney Swans have suffered a blow on the eve of the premiership season, with ruckman Sam Naismith injuring his knee at training on Wednesday. 

Scans have revealed the 25-year-old ruptured his anterior cruciate ligament during a training drill at Lakeside Oval.

Swans Head of Football Tom Harley said it’s clearly a disappointing outcome. 

“Obviously this is a disappointing setback for Sam so close to the start of the new season,” Harley said.

“Sam was involved in a fairly routine training drill when his knee innocuously twisted, causing a rupture of his anterior cruciate ligament.

“While this is an unfortunate injury for Sam, we know he’s an absolute professional when it comes to his preparation and recovery and he will no doubt do everything possible to make sure he recovers from this injury.”

Naismith will undergo further medical assessment before deciding on the next course of action.