No big sports earner has ever given a major sum to charity, he said, even though the top 200 Premiership players earn £200m a year between them.
"Your 20s is the worst time to have lots of money," Beresford told delegates to Action Planning's Raising Funds from the Rich conference. "People that age are concerned with earning as much as possible while they are at the top. The collision of having a lot of money with testosterone means if they are not sensible they either blow it or snort it.
"But if you want them to be the PR front of your charity, they are invaluable."
Beresford said sportsmen might become more charitable after they retire, but by then they no longer earn as much as before.
"It will be interesting to see if David Beckham will become a charitable role model after his sporting career," Beresford said.