Kostjasyn, 30, sustained the complex injury in a freak training-ground accident early in the year. 

He was initially set to miss around three months, but despite undergoing a number of surgeries to repair the injury, his airways have been significantly narrowed.

“Retirement was a combination of medical advice and how my body was unable to adapt to a reduced airway,” Kostjasyn said in a statement.

“It has by far been the most challenging six to seven months I've faced, not only in my career but in everyday life.

“Unfortunately, it's a challenge that I've been unable to overcome.”

Kostjasyn never even had the chance to play for Newcastle after joining the club this year following a stint with the North Queensland Cowboys. 

He retires after making 126 NRL appearances for the Cowboys and Melbourne Storm, including a Premiership with the former. 

“It hasn’t fully sunk in that I am retiring yet,” he added.

“I'm still frustrated every game day that I can't run out and play.

“When I reflect, I have been lucky to be a part of some great clubs and playing groups.

“I wasn't fast, big or super skilful but I just worked very hard to do my job for my teammates.

“Apart from not getting to play for the Knights, I can’t think of too many regrets.”