FREMANTLE has locked away Brennan Cox until at least the end of 2024 after the defender put pen to paper on a two-year contract extension.

The 23-year-old has become a mainstay in the Dockers defence in recent years, playing 59 games in his five seasons at the club.

He managed 12 games in 2021 before a serious hamstring injury in round 12 ended his season early.

"It feels really good (to sign on), I'm really excited about the group we have and the way the future is looking," Cox said.

"We've got a really good bunch of boys and I'm excited to grow as a player and get stuck into this season."

Cox is expected to be available for full training when the five-year-plus players return to pre-season on December 6.

"It's obviously not ideal getting the hammy and it's been a long process to get back to full strength, but I'm there now," he said.

"It's been a long off-season, but the hammy is fully healed and I'm ready to go."

Drafted as a versatile key-position player, Cox made a permanent switch to defence last year and is expected to play a similar role in 2022.

"If a tall forward goes down I might have to swing forward and kick a few goals, however, at this stage I'm a defender," he said.

"It's always good getting some new boys in (via the draft), as long as they don't draft anymore defenders because I don't want to be put out of a spot!"