Fremantle's hopes of snaring an AFL top-four berth were dealt a severe blow on Monday after star defender Chris Tarrant was ruled out of the rest of the home and away season.

Tarrant is set to miss up to six weeks after injuring his medial ligament in Sunday's 75-point derby win over West Coast.

The 29-year-old had missed the previous five weeks with a heel complaint and will have to rely on Fremantle going deep into September to have a realistic chance of playing again this year.

Tarrant, who spent the majority of his career as a forward, has become arguably Fremantle's best defender over the past two seasons and his loss will be sorely felt as the fifth-placed Dockers strive to finish off the season strongly.

But Fremantle, whose injury list includes star midfielder Michael Barlow (broken leg), Ryan Crowley (knee), Chris Mayne (ankle) and Alex Silvagni (groin), face an uphill battle to leapfrog the fourth-placed Bulldogs and earn a double finals chance.

In better news, midfielder Rhys Palmer (shoulder) and back-up ruckman Kepler Bradley (knee) are strong chances to return for Saturday's crucial clash with North Melbourne at Etihad Stadium.

And in-form Fremantle goalsneak Hayden Ballantyne is keen to continue his knack of demoralising opponents.

Ballantyne, who has been caught on camera pinching Gary Ablett and pulling the hair of Harry O'Brien, has laid 58 tackles this year and believed his desperate acts in the forward 50m gave the Dockers a vital edge.

"When you chase someone down you demoralise the opposition as well and then we get a goal and it lifts us," Ballantyne said.

"That's definitely one of the great things about our game, to be able to chase someone down from behind and it just kills the opposition.

"It's been drilled into all of us; put pressure on, force the turnover and punish them on the offensive as well."

Ballantyne has quickly become a fan favourite at the Dockers, with his six-goal haul against the Eagles only helping his cause.

But the 23-year-old almost missed out on an AFL career after being overlooked in two national drafts.

Fremantle took the punt on Ballantyne with pick No.21 in the 2008 national draft and the tenacious 174cm forward has repaid the club in spades.

"I was always hoping I was going to get a chance and I was lucky Freo gave me the chance," Ballantyne said.

"I knew it was going to take a lot of hard work and I was a bit edgy on whether I was going to get picked up.

"The more you miss the harder you want to work and try get to it.

"So far I haven't missed a game (this season), so I suppose it is a dream season.

"I just want to play every game and keep doing my part for the team."

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