Nigel Currie, director of sports marketing agency Brand Rapport, said: "He has the potential to do what Roger Federer, Michael Schumacher and Tiger Woods have done.
“Golf, motor racing, boxing and tennis are the big-earning sports.
“If he was to dominate golf, like he could do, for a number of years, he could get up towards the one billiondollar mark.
He added: “He is so young and a precocious talent. The youthfulness gives him a unique factor and he comes across very well.
“He has put himself right in pole position and the next stepping stone is to establish himself as number one for a period of a few years.”
Steve Martin, chief executive of M&C Saatchi Sport and Entertainment, said: “Over the next 10 years he is going to be the £100million man – not dollars, pounds.
“It is that scary.
“But there are few sportsmen with the potential to transcend the sport. Up until last night Rory McIlroy was always an amazing young golfer.
“Now he is an amazing superstar sportsman and the potential to double his earnings is very, very realistic.
“His appeal is unusual because he is so young.
“He has broken all those records and Irishmen in America go down very well.
“He has got everything in his locker – youth, he handles everything well, he smiles, he is engaging to listen to and he is incredibly aspirational for young kids.”