The 20-year-old, who was one of the stars of the Jets’ drive to the grand final last season, had surgery in Newcastle on Monday to remove the thyroid gland and requires further treatment in coming weeks.

The right back noticed a lump at the bottom of his throat earlier this month and was sent for scans by the Jets’ medical staff.

In a statement on Wednesday, the Jets said the prognosis on Koutroumbis’ was “very good” due to the early detection of the tumour.

His family have travelled from Adelaide to help with his recovery, and the Jets and players union have pledged their full support.

The news has rocked the club on the eve of the season.

“Johnny has a wonderful family who are right behind him, but our entire club and the football community will also be with him every step of the way,” Jets football operations manager Joel Griffiths said.

“We’ve been advised the prognosis is good and it [the cancer] is very treatable, especially given this has been caught so early.

“Johnny originally reported a lump at the base of his neck to Nathan Renwick (club physiotherapist) and he was sent for scans.

“Early intervention in these scenarios is important, it’s great that this was able to be found and Johnny can now receive the treatment he needs. 

“We won’t be placing any timeframe on his recovery at this point, we’re just wanting to make sure he gets all the treatment and support he requires.”

Koutroumbis was training with the squad up until Friday. 

Lachy Jackson is likely to replace Koutroumbis at right fullback for the Jets season opener against Wellington at Westpac Stadium on Sunday.