THE SYDNEY Swans' finals campaign could have been dealt a severe blow even before it begins, after co-captain Kieren Jack injuring his knee late in the first quarter of Saturday's clash against Gold Coast.

The incident occurred in the centre square of the SCG, when veteran Sun Danny Stanley and Jack collided at the centre bounce.

Stanley's shoulder appeared to make contact with Jack's left knee and the Swans midfielder immediately fell to ground.

Jack was assisted off the field and after a quick assessment was given the red vest, and looked a very disappointed man on the interchange bench at quarter-time.

Swans' substitute Lewis Jetta was activated.

The Swans need to win to hold down fourth spot and a double chance in the first week of the finals.

Meanwhile, Sun Greg Broughton's AFL career has had a premature ending after he was substituted out in the first quarter with what looked like a leg injury.