LACHIE Whitfield is irreplaceable.

There isn't a player like him lurking in Greater Western Sydney's NEAFL stable because there's nobody in the competition who can influence games of footy in the ways that he does.

Whitfield might be, pound for pound, the most talented player in the game.

Lachie Whitfield will sit out this week's preliminary final with appendicitis. Picture: AFL Photos

So, how can the Giants possibly cover his absence, due to a bout of appendicitis, in Saturday's preliminary final against Collingwood at the MCG?

Look no further than his best mate, Zac Williams.

Inseparable off the field, Whitfield and Williams have been stars for the Giants at different ends of the ground this season, but they bring vastly different qualities to the team on game day.

That could be the Giants' trump card against the Pies.

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Whitfield is a phenomenal two-way runner who covers enormous territory as a high half-forward, and has sublime skills on both sides of his body.

The 25-year-old picks holes in the opposition all over the field and isn't just a vital link player for the Giants, he's often involved multiple times in his team's transition from the backline to the forward half.

Williams probably doesn't have the tank to have that impact against the Pies.

What he can do is bring his own unique strengths to the role and that makes him an equally damaging weapon for GWS, and just as dangerous for the Magpies.

The 24-year-old uses leg speed and raw power to burst from half-back, and has creativity and attacking flair to make exciting things happen when he has the footy in his hands.

He's the No.1-ranked player at GWS for average metres gained – Whitfield is second - and ninth in the competition.

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Williams loves to run and while he's cavalier at times, he's smart enough to see openings where other players might not and charge through them, which unsettles the opposition.

He's also adaptable and that will be the key to GWS winning this week.

The Giants switched his role late in the season when their midfield was decimated with injury, and he dominated in the absence of Josh Kelly, Stephen Coniglio, Callan Ward and Matt de Boer.

It showed he's comfortable in traffic and also a clearance threat.

He has the vision and footy smarts to be a full-time onballer and probably would be at any other club, so there's little doubt he has the ability to fill in for Whitfield, who has a licence to roam from coach Leon Cameron.

He starts inside 50 then gets involved at stoppages up the ground, or moves himself to a wing if he likes a match-up.

Williams has the intelligence to also thrive with that freedom.

Williams and Whitfield are good friends, on and off the field. Picture: AFL Photos

If Cameron decides to give his dashing half-back a different look, it would leave a hole in defence no doubt, but in Heath Shaw, Adam Kennedy, Harry Perryman, Sam Reid and Isaac Cumming, the team can cover Williams to an extent.

The presence of co-captain Phil Davis as the general and chief organiser will help with that.

If Toby Greene is missing due to suspension, Williams can also add the hardness and aggression at the footy that the star forward brings to the Giants inside 50.

Whitfield is irreplaceable, but that doesn't mean the Giants can't throw Williams at Collingwood to give them a headache of a different kind.