A leading expert has warned that children's brains can be damaged by heading footballs at an early age.
Dr Ann McKee is a neuropathologist at Boston University and has extensively researched head injuries in the NFL.
"I think there are dangers to the adolescent brain being exposed to these injuries," she told BBC World Service.
"Before the brain is fully developed, before the neck and musculature is mature I think these kids are at risk."
In America, a study of 24 American football players aged between 16 and 18 found abnormalities similar to the effects of mild traumatic brain injury after one season.
Former England and West Brom striker Jeff Astle died aged 59 in 2002 from a brain condition called chronic traumatic encephalopathy (CTE), which is normally linked to boxers.
Astle was incorrectly diagnosed with Alzheimer's but earlier this year Dr Willie Stewart analysed Astle's brain and highlighted CTE, a progressive degeneration of the the brain caused by repeated head trauma.
He added that a number of footballers could be affected by the condition.
Former WWE wrestler Chris Nowinski, founder of Sports Legacy Institute, told BBC World Service: "No child under the age of 14 should be heading a football.
"The reality is that no child under the age of 14 should be receiving intentional brain trauma, it doesn't matter what sport.
"One header is not dangerous, however a lifetime of thousands of headers is dangerous. It does appear to increase your risk of later life problems."