A new study has revealed football players are at high risk of brain damage, dementia and depression due to repeated head injuries.

The study from the United States is the latest to make the link between concussion and brain conditions and could leave professional football codes in Australia vulnerable to legal action.

The study has already seen over 4000 former gridiron players sue the National Football League for damages.

Scientists at the University of California Los Angeles performed brain scans on living ex-players to establish a link between head knocks and brain conditions.

Previous studies could only be conducted post mortem.

The research established players who had suffered multiple concussions during their career displayed high levels of the trace protein tau, which indicates a high risk of brain conditions.

Dr Samiul Sorrenti from the Rugby League Medical Officers Association says even the accumulation of minor concussions during a career can add up to a serious injury.

"The most important thing is that any contact with the head should be avoided," he told news.com.au.

"When the brain recoils forward it can cause micro-damage. If you get this repeatedly over a period of time it causes macro-damage.

"Premature dementia is the major thing that's going to worry us.

"What we don't want to see in 20 years time is ex-footballers having an increased incidence of dementia or other mental problems and when we look back - it was due to the number of injuries we have."

Former North Queensland Cowboys rugby league player Shaun Valentine has spoken openly about the long-term effects of concussion.

Valentine, who has pledged to donate his brain to research after his death, says he suffers severe memory loss after his career was cut short due to several severe head knocks.

Last year the National Rugby League outlawed the shoulder charge, which is a tackle that often results in heavy contact between a defender's shoulder and the attacking player's head.

The NRL's decision came after several shoulder charges last season resulted in heavy concussions.

Shoulder charges are already outlawed in rugby union.

The issue of concussions created headlines in the AFL last season when Adelaide Crows rested their star forward Kurt Tippett for three matches after he suffered three concussions in the space of five weeks.

Tippett has since moved clubs to premiers Sydney, who say Tippett's history of concussions was not a factor in their decision to sign him.

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