Stefan Okunbor in action for the VFL team last year. Picture: geelongcats.com.au

GEELONG defender Stefan Okunbor is set for a long stint on the sidelines after rupturing his Achilles tendon at training this week.

The 21-year-old Irishman will be put under the knife on Sunday for immediate surgery after meeting with a specialist in recent days.

Okunbor suffered the setback on Wednesday and will put the remainder of his 2020 campaign in doubt.

It is a further blow for the Cats, who still have captain Joel Selwood (hamstring), Mitch Duncan (hip/shoulder), Tom Stewart (groin) and Jake Kolodjashnij (hip) and Mark O'Connor (toe) in the rehab group.

The Category B rookie can take heart from Greater Western Sydney defender Zac Williams' recovery from the same injury in 2018, after going down in January and returning in August.

Okunbor joined the Cats ahead of the 2019 season and played eight VFL matches last year.

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