Frederick, who has South Sudanese heritage, re-posted the racist message on his Instagram account.
Dockers chief executive Simon Garlick said the club would not tolerate the continuing racial vilification of AFL players.
"This abhorrent comment is just one example of the racist abuse many in Australia experience in their everyday lives. The Fremantle Football Club and our broader Fremantle Family stand by Michael for calling out this type of abuse," Garlick said.
