Fremantle has been dealt a major blow before its clash with Geelong on Sunday, with superstar Nat Fyfe ruled out with a bruised sternum.

The AFL sent out a tweet just before 11.30am on Friday saying the Brownlow Medallist had 'withdrawn' from the game with the Dockers formally confirming it was due to the injury just before midday.

Fyfe has played the past month with a substantial chest injury that has required him to wear a protective vest to help him get through games.

And the Dockers confirmed bruising in the area was the reason for the late omission.

General manager of football operations Chris Bond said the club was confident the superstar would recover in time for Fremantle's round 15 game against St Kilda on Sunday week, but conceeded the situation would need monitoring.

"The medical advice was that Nat be ruled out this week," Bond said.

"We will monitor Nat throughout next week before making a final decision but we believe he will be right to play in the St Kilda game."

Rebounding defender Cam Sutcliffe comes into the squad to replace Fyfe, which will be cut to 22 on Friday afternoon.

WAtoday sports writer and Radio 6PR football commentator Kim Hagdorn flagged last week the 25-year-old had endured agonising pain with severe bruising high into his chest cavity since early last month.

The gun ball-winner wore a guard under his jumper, which was noticeable for the first time in the Dockers inglorious 57-point loss to last-placed Lions, when he gathered just 18 disposals from 11 kicks and seven handballs, with two first-half goals.

Fyfe has also nursed substantial bruising in his thighs after a torrid opening half of the season, with the first-year Dockers captain averaging around 26 disposals an outing as his side's second biggest possession-winner so far through the home-and-away campaign.

Dockers management and Fyfe have constantly denied he has been nursing any injury.

Despite the injury, Fyfe has continued to collect hefty disposal totals, with around 60 percent of all his possessions won in a direct contest.

Fyfe's overall game time has dropped marginally from around 92 percent an outing up until the round five win over North Melbourne in Perth, to 86 percent a week since a loss to West Coast at the end of April.

The 2015 Brownlow medallist's contract remains a priority for the Dockers, with Fyfe yet to announce whether he will re-sign with Fremantle beyond 2017.

The champion on-baller has been at the centre of constant speculation that his playing value and productivity has substantially declined this season on his return from a broken leg which saw him miss almost the entire 2016 season.

Fyfe is a restricted free agent and is attracting offers well in excess of $1 million a season to leave Fremantle and continue his career, most likely in Victoria.