Young Sharks forward Fine Kula is being treated in Liverpool Hospital after being diagnosed with brain cancer.
The 21-year-old front-rower, a former NSWRL Matthews Cup Player of the Year in 2015 and Jersey Flegg premiership winner in 2018, had been training with the first-grade squad before Christmas.
After a series of headaches, tests revealed Kula was suffering brain cancer and he has been forced into an early retirement.
"The Sharks are offering their full support to Kula and his family at this difficult time, with details being worked through, in consultation with the Men of League Foundation, regarding fundraising activities aimed at assisting with the on-going costs associated with his treatment," the club said in a statement.
"The Cronulla Club, NRL coaching staff and the playing group are rallying around Kula and his family, with Sharks welfare staff also providing support and assistance."