Defender Aliir Aliir faces a nervous week if the Sydney Swans translate their first-half dominance of Geelong into a Grand Final berth, after suffering a game-ending knee injury in Friday night's second preliminary final at the MCG.

Aliir landed awkwardly after a marking contest with Cat Lincoln McCarthy late in the first quarter, and appeared to hyperextend his right knee.

The Swans defender had tape applied above and below his knee at quarter-time, and did some run-throughs along the boundary line early in the second term.

Despite moving more freely by the end of his fitness test, Aliir's night was over before half-time when he applied an ice pack to his knee late in the second term.

With the Swans leading by 49 points at the main break, the 22-year-old almost certainly faces a race against time to prove his fitness for next Saturday's Grand Final.

Swans co-captain Jarrad McVeigh (calf) will also be striving to prove his fitness after being ruled out of Friday night's game.