Heading a football affects memory and brain function for at least 24 hours, a new study has found.
Researchers from the University of Stirling found "immediate and measurable alterations in brain function" after players head a ball, according to results published in EBioMedicine.
Memory test performance was reduced between 41 and 67% after routine headers, with effects normalising within 24 hours.
The results raise concerns about the long-term impact of repeated heading during training sessions and matches for professional players.
In the US, the American governing body of football has banned players under the age of 10 from heading the ball over concerns about concussion.
The findings come after concerns that players' brains are damaged by repeated head impacts.
Former England and West Brom striker Jeff Astle died in 2002 at the age of 59 having suffered from early on-set dementia, which a coroner found was caused by heading footballs and gave the cause of death as "industrial disease".
A subsequent re-examination of Astle's brain found he was suffering from the neuro-degenerative brain disease chronic traumatic encephalopathy (CTE).
CTE can only be established following death and it has also been found in deceased American footballers, boxers and rugby players.
Astle's daughter Dawn has been campaigning for more research into the matter and was told by the Football Association and the Professional Footballers' Association in late 2014 that they were talking to Fifa.
The University of Stirling study was conducted by firing footballs from a machine at nineteen amateur football players at standardised speeds that were modelled on routine soccer practice.
The brain function and memory for each player was then tested immediately and again at 24 hours, 48 hours and two weeks later.
Scientists noticed a significant reduction in memory function which lasted for at least 24 hours but added that more research was needed to discover any possible long-terms affects of heading a ball.
Dr Angus Hunter, from the university's Faculty of Health Sciences and Sport, said: "For the first time, sporting bodies and members of the public can see clear evidence of the risks associated with repetitive impact caused by heading a football.
"We hope these findings will open up new approaches for detecting, monitoring and preventing cumulative brain injuries in sport.
"We need to safeguard the long term health of football players at all levels, as well as individuals involved in other contact sports."