GEELONG has taken Mitch Duncan off next year's free agency list after giving the star midfielder a four-year contract extension.

Already contracted for next season, the fresh deal secures Duncan's future at GMHBA Stadium until the end of 2024.

The West Australian is due to become an unrestricted free agent at the end of 2020 but remains settled in Geelong with his young family.

Due to turn 33 in 2024, the deal would ensure the premiership Cat is a Geelong footballer for life and could see him pass the 300-game milestone after playing his 200th in round 19 this year.

It would continue a trend of long-term contracts at the Cats. Joel Selwood, Tom Hawkins and Mark Blicavs all signed deals in recent seasons keeping them at the club beyond their 32nd birthdays.

Duncan would have been part of a bumper crop set for free agency across the competition at the end of 2020 that includes Giants pair Jeremy Cameron and Lachie Whitfield, Crow Brad Crouch and Bomber Joe Daniher.

Collingwood's Brodie Grundy is on the verge of re-committing to the Pies on a new seven-year deal.

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Other key Cats set to fall out of contract at the end of 2020 include Hawkins, Quinton Narkle, Sam Menegola, Brandan Parfitt and Rhys Stanley.

Quinton Narkle and Patrick Dangerfield share a laugh at training on Tuesday. Picture: AFL Photos

Duncan returned to Geelong training this week with the Cats' first-to-fourth-year players, a fortnight earlier than he was officially required back at the club. 

After averaging 25.3 disposals in 2019, the 29-year-old missed final two matches of the Cats' campaign with a medial ligament injury.

Meanwhile, forward Gary Rohan has extended his contract with the Cats until the end of 2021. 

The former Swan booted 25 goals in 19 games in his first season at Geelong.

"Gary was able to enjoy a strong start to his career in Geelong colours at the beginning of the season. He made a smooth transition into our team and was an energetic addition to the group both on and off the field," general manager of football Simon Lloyd said.