Talented pupils worry that they will be ostracised by peers who are jealous of their ability, according to a survey of more than 1,000 eight to 14-year-olds.
Winning imposes a "psychological burden" on pupils, marking them out as different at a time when they are under social pressure to conform, the report says.
The research was carried out for Norwich Union, the financial services company and major athletics sponsor, in response to concerns that young people are becoming less active.
Almost a third of young people are now either overweight or obese and Sport England estimates that the number of young people not regularly taking part in sport has increased from 15 per cent in 1994 to 18 per cent last year.
"At an age when being different is unacceptable among your peers, winning as much as losing, could result in them losing friends and being less popular," the report says.
"This reluctance to win is not mirrored in countries like Australia where sports success is a source of immense national pride," it added.
But Oliver James, a child clinical psychologist, said that the findings showed that taking part was still as important as winning. "In this country we have traditionally celebrated events such as Dunkirk or losers such as Eddie the Eagle. One could argue that this shows that our culture has survived the attempts of first Thatcher and now Blair to turn us into ruthless driller killers.
"My only concern would be if this is a result of envy, of children not wanting anyone to be better than anyone else."
The survey also found that a majority of pupils in primary schools and most secondary school boys would like to do more sport in schools.