NAT Fyfe's Brownlow Medal chances have taken another hit with the star midfielder ruled out of Sunday's clash with St Kilda.

It is the second consecutive match Fyfe will miss after failing to overcome a groin issue.

Fyfe is the raging Brownlow Medal favourite and is as short as $1.75 with bookmaker Crownbet.

But Fyfe's rivals are closing with Swans midfielder Dan Hannebery scoring a perfect 10 in the AFL Coaches Association votes for round 18 and moving within 15 votes of Fyfe on the leaderboard.

In Brownlow Medal betting, reigning Brownlow medallist Matt Priddis is second favourite at $5.50 and Hannebery is third at $7.

In the past 20 years only three players have missed two or more games within a season and gone on to win the Brownlow: Chris Judd (played 19 games in 2010), Gary Ablett jnr (19 in 2009) and Jimmy Bartel (20 in 2007).

Coach Ross Lyon said last Sunday Fyfe was a 50/50 chance to return against St Kilda this week.

Fyfe underwent a lengthy fitness test on Wednesday at Fremantle Oval, but on Thursday the club confirmed on its website that he would not play against the Saints. 

Fremantle's football operations manager Chris Bond said the club was hopeful Fyfe would be available to face West Coast in round 20.

"We are hopeful that Nat will be right to play next week," Bond told fremantlefc.com.au.

"We will assess the situation during the week, after which we will be better placed to make a decision about Nat's availability."

Fyfe appeared to move reasonably freely during his fitness test on Wednesday.

The session, which ran for over 45 minutes under the watchful eye of Dockers' sports science manager Jason Weber, included side-to-side agility work interspersed with running over distances varying from 50m to 150m to 300m.

He never hit top pace although the session appeared to be more volume-based rather than speed-focussed.

Fyfe now has 10 days to try and be fit for the Western Derby on Sunday August 16.