Cox, 19, made in his debut for the Dockers in Round 12 and has played the past five matches, while Ryan made his debut in Round 11 and has played the last six games.
“Brennan and Luke are good young men who are very much a part of the long-term future of the club,” general manager football operations Chris Bond said.
“The players have set and agreed to standards, which all of our players are required to adhere to. However, on this occasion that was not the case.
“As a result, Brennan and Luke were not selected in the team to play Hawthorn on Saturday.”
Fremantle host the Hawks at Domain Stadium at 5.40pm AWST on Saturday.