Fremantle defender/midfielder Matt de Boer will become the club's fourth player to debut this year when he runs out in Saturday's western derby at Subiaco Oval.

De Boer, elevated to the senior list during the pre-season, will replace the injured Rhys Palmer, who has been ruled out for the rest of the season after tearing his anterior cruciate ligament against Sydney last week.

Fremantle coach Mark Harvey said de Boer, 19, had a mature body ready for the rigours of senior football.

"It's a big occasion for him," Harvey said.

"He's a product of WA football, coming from grass roots, playing at Claremont, being on the rookie list and now playing his first game for Fremantle against West Coast.

"He's got a more seasoned body than a lot of other guys we've got just out of the side at the moment.

"He's got a good temperament and he's got this exciting nature about him that can really enthuse the side.

"I'll ask him to fill a role and hopefully he can do that.

"Every club goes through injuries but when you lose one of your star midfielders like Rhys it can be difficult so it puts pressure on other guys to fill the void in that area."

De Boer's inclusion follows the debuts of Nic Suban, Stephen Hill and Greg Broughton earlier in the season.

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