FREMANTLE coach Justin Longmuir has called on fans to watch their mouths in the wake of the abuse levelled at Michael Walters over the weekend.

Walters was verbally abused by a West Coast fan while walking off the field after Fremantle's shock 37-point Western Derby loss on Saturday night.

Although the abuse wasn't racial in nature, it overstepped the mark of what is appropriate at a football match, West Coast acknowledged.

The Eagles have reached out to Walters to lend their support to the veteran in the wake of the "crude and offensive remarks".

The AFL and Optus Stadium are investigating the matter.

"It's frustrating for anyone to walk off the oval at the end of the game and cop abuse ... in pretty ordinary language," Longmuir told reporters on Wednesday.

"It shouldn't happen. And it's not just one fan – it's a thing across the League, something we need to temper.

"Players should be able to feel safe walking on and off the field, as should coaches and all staff.

"I understand the passion in the game. That's what drives footy to be as great as it is.

"But we need to make sure we temper that passion, and instances like that shouldn't happen."

Longmuir had a simple message for fans.

"Support your own team loudly, but watch what comes out of your mouth when it comes to opposition players," he said.

"They're humans, and they deserve to be treated like it."

Walters started the season in strong fashion, but has endured a huge form slump over the past three weeks in a period that has coincided with Fremantle's losing streak.

The 33-year-old kicked one goal from seven disposals against Carlton, was goalless from five disposals against Port Adelaide, and was restricted to one goal from seven touches against West Coast.

With small forwards Michael Frederick (hamstring) and Sam Switkowski (concussion) strong chances to return for Saturday night's home match against the Western Bulldogs, there's talk Fremantle should send Walters back to the WAFL.

But Longmuir hinted that Walters will be retained in the senior side.

"We need to get 'Sonny' going. We need to get him more footy and more involved in the game," Longmuir said.

"A lot was made of our forward line on the weekend, but realistically we didn't give them enough supply.

"That's on the other lines to make sure we get the ball in our front half and give our forwards more opportunities."

Defender Heath Chapman could make his first AFL appearance since round three last year after making a successful WAFL return in recent weeks.

But spearhead Jye Amiss (concussion) will miss the match against the Bulldogs, opening the door for Matt Taberner's return or an AFL debut for former Bomber Patrick Voss.