By conducting autopsies on two former rugby league players a leading Sydney researcher has discovered a degenerative brain disease associated with repeated head trauma.

Key points: Chronic Traumatic Encephalopathy (CTE) has never before been identified in rugby league players

Chronic Traumatic Encephalopathy (CTE) has never before been identified in rugby league players Autopsies were conducted on two ex-professionals who each played 150 games of first-grade NRL

Autopsies were conducted on two ex-professionals who each played 150 games of first-grade NRL The NRL has tightened guidelines to manage player concussion in recent years

The landmark finding is the first time Chronic Traumatic Encephalopathy (CTE), colloquially known as being "punch drunk", has been identified in rugby league players anywhere in the world.

Associate Professor Michael Buckland, from the School of Medical Sciences at Sydney University, said both men were middle-aged ex-professionals who had each played more than 150 first grade NRL games over many years.

"Case one had a successful career after retirement and had been working up until his death. He did not abuse tobacco, alcohol, or other drugs," Associate Professor Buckland wrote in his research.

However, his family members reported an increasing reliance on aide-memoires for daily activities in the years prior to his death, and difficulties remembering details of a significant life event.

"Case two had some issues during his transition to a post-playing career, but was productively employed up until his death," Associate Professor Buckland wrote.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 22 seconds 2 m 22 s Researchers say the extent of brain injuries from contact sports are unknown. (Photo: AAP)

In recent years, the NRL has released stringent guidelines for the management of concussion based on outcomes from the 2016 International Conference on Concussion in Sport.

In those guidelines, the NRL states that the welfare of the player, in the short and long term, is the most important element in the management of concussion.

Players who suffer a concussion need to undergo a strict head injury assessment (HIA), and are not allowed to return to training or playing until cleared by a doctor.

According to the NRL, a concussion occurs once in around three and a half matches.

The deadly disease was thrust into the public domain as a result of the 2015 film Concussion starring Will Smith, which was based on a forensic pathologist's fight against America's National Football League who attempted to cover up his research on repeated head injuries on players.

Associate Professor Buckland's research was published in the online journal Acta Neuropathologica Communications.