NIC Naitanui's season is over after scans confirmed the star ruckman has ruptured his anterior cruciate ligament in his left knee.

West Coast feared the worst on Friday night after Naitanui landed awkwardly on his left leg in the third term of the 25-point win over Hawthorn.

Naitanui had scans on Saturday morning and the club confirmed just hours later the bad news. The 26-year-old will require a knee reconstruction and will meet with surgeons this week to determine the best course of action.

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It's a massive blow to the Eagles' premiership hopes this season, but will also have significant ramifications for 2017 and beyond given he is likely to miss the majority of 2017.

His left leg is his jumping leg at centre bounces and his ability to regain his greatest strength after a long rehabilitation will be a great unknown.

The Eagles tried four different ruck combinations when Naitanui was missing but coach Adam Simpson conceded on Friday night he was not settled on a definitive back-up plan.

Scott Lycett combined with Mitch Brown, Jonathan Giles and Jeremy McGovern in different games, while Giles partnered Fraser McInnes when Lycett was out for a club-imposed suspension in round 13.

McGovern's value in defence was highlighted by what happened the Eagles when he rucked during the loss to Collingwood in round 19.

Brown would appear the best option given his competitiveness in the wins over Essendon, North Melbourne and Carlton but he is severely undersized at 195cm and had never previously rucked.

Lycett will carry a huge load. He is also battling some soreness after suffering a corked thigh against the Giants and knee knock against Hawthorn. 

Simpson warned critics not to write off the Eagles for 2016 after their win over the Hawks but Naitanui's influence cannot be undersold.

The Eagles have won seven of their last eight, including five without Naitanui while he was out for a six-week block following surgery to remove both plantaris tendons.

But they had to find other ways to win given how much of an advantage they lost in key areas without Naitanui.

Without Naitanui, the Eagles 

- Slumped from first to last in the AFL in hit-outs to advantage differential (+7.9 to -7.7)

- Dropped from first to 17th in hit-out differential (+23.2 to -17.8)

- Dropped from fifth to 18th in clearance differential (+1.9 to -6.2)

- Second to 17th (+3.0 to -2.8) in centre bounce clearance differential

- Slumped from sixth to 15th in contested possession differential (+3.3 to -10.2)

In Friday's 25-point win over the Hawks the Eagles were +45 in contested possession, +12 in clearances and +9 in centre bounce clearances.

Naitanui also kicked the match-winner from a forward 50 stoppage with seconds remaining against Greater Western Sydney in round 21.