Mundy was a late withdrawal from last week’s game against North Melbourne, while Barlow had a procedure on his jaw after copping a knock in that game.
Both were given until Thursday morning’s training session to prove their fitness, but Lyon said from Perth airport that the pair would not be risked.
"We try and look after the players' best interests," he said.
"That's the way we go about it. We always put our players' personal welfare as the number one priority."
Lyon said second-year player Tom Sheridan would play against the Cats. Sheridan played one game in his debut season.
Stay tuned to fremantlefc.com.au for The Freo Line-Up at 4.25pm
