ST KILDA will be forced to stage a second-half comeback against Melbourne without midfielder Koby Stevens, who has been ruled out of Sunday's all-important battle at the MCG with concussion and a burst ear drum.

Stevens came off second best in a head clash with Melbourne's Angus Brayshaw in the first quarter of Sunday's game.

The Saints' midfielder was assessed for concussion in the rooms and did not reappear on the bench by the end of the second term, meaning his day is done.

Making his return from almost two months out following his fourth concussion in 12 months, the clash with Stevens was a frightening incident for Brayshaw, who is wearing a protective helment, and Melbourne's medical staff.

Fortunately the Demons' midfielder bounced up to his feet after the shock of the hit wore off, and he does not seem to be adversely affected by his latest head knock.

Playing his first senior game since round two, Brayshaw has been one of Melbourne's best players with 15 disposals to half-time.

The Demons booted six goals to one in the opening term to seize control of the contest and lead the Saints, who finally struck a blow in the second term with three goals of their own, by 32 points at half-time.

Sunday's game is huge for both teams, with the loser of the game all but out of the finals hunt.