The 40-year-old, who won gold in Sydney 12 years ago, said that Joshua has the ability to finish on top of the podium at London 2012, but reminded the 22-year-old that he has got to work hard for it.
"I rate him a lot," said Harrison. "He's young and hasn't got a lot of experience, but what he has is tremendous ability and I'm really looking forward to him going all the way.
"He has a great chance of winning the gold. He's got to go out there and earn it - they're not going to give it to him - but he has a great chance. The world's at his feet.
"I'm going down there for the semis and the finals and I'm really looking forward to seeing our boxers perform."
Joshua takes on Kazakhstan's Ivan Dychko tomorrow for a place in the final.