North Melbourne's 48-point win over Melbourne on Saturday at the MCG came at a cost, with key defender Josh Gibson suffering what could be a serious knee injury.

Gibson spoiled from behind in a marking contest midway through the third quarter but may have hyper-extended his knee as he landed awkwardly, although he did also then collide with team-mate Sam Power when the ball hit the ground.

A week after trying hard but conceding five goals to Hawthorn superstar Lance Franklin, Gibson was doing a superb job on Demons forward Russell Robertson, who to that point had not kicked a goal.

His team-mates up the field may have assisted his performance on the lively Robertson, with the delivery to the Melbourne forward poor for much of the game, but Gibson's efforts looked even more impressive when Robertson booted three final-quarter goals.

North medical staff gave little away during the game, other than to confirm that Gibson had suffered the knee injury, but the defender spent the rest of the game sitting on the bench pondering his immediate future.

The loss of Gibson for an extended period could prove disastrous to coach Dean Laidley and his plans for the year, although Laidley was able to cover the absence of Gibson for a couple of months in 2007.

Gibson missed a long stretch after fainting in his bathroom and hitting his head on the sink as he collapsed, suffering bleeding in several places in his brain that initially had him fearing his career may be over.

The 24-year-old did bounce back to full fitness ahead of schedule and return in time for the finals, restricting Franklin's impact in the semi-final as the Kangaroos beat the Hawks, and will be hoping to repeat that fast recovery from this latest setback.