WEST Coast has been dealt a serious blow ahead of the home and away season after scans confirmed defender Eric Mackenzie will need a knee reconstruction.

The 26-year-old tore his right anterior cruciate ligament in the Eagles' NAB Challenge win over Carlton on Friday night, after falling to the ground in an innocuous marking contest.

Coach Adam Simpson said after the game the club was fearing the worst and those concerns were confirmed on Saturday following further assessment.

The club said in a statement that Mackenzie, who beat Brownlow medallist Matt Priddis for the club's best and fairest last year, will wait for swelling to subside before he has surgery this week.

It is a shattering loss for the Eagles, with Mackenzie their first-choice key defender and a vital cog in their backline.

He has played 71 of the past 75 games for the club and was rotated through the captaincy last year after the retirement of fellow defender Darren Glass.

Mackenzie's rise as one of the competition's most consistent defenders has been acknowledged as a nominee for the 2013 and 2014 All Australian squads.

The injury took the gloss off the Eagles' convincing 31-point win over the Blues.

They will continue their NAB Challenge series against Port Adelaide on March 8 and then face Fremantle on March 22 in their final hit-out before round one.