American Leonard, a world champion in four different weight divisions, is confident Khan will one day break into the big-time across the Atlantic.
"From what I hear from the boxing community, he is a huge prospect," Leonard said.
"He has the chance to cross over to the American market, and that is when you really make a huge impact."
That has greatly excited Bolton's Khan, who said: "Sugar is a boxer I have always looked up to.
"I still watch his videos and try and copy some of the things he did in the ring. For him to say I am a special boxer and can be a champion is fantastic.
"My preparations for my next fight are going really well. It's just about making the weight and I'm just itching to get into the ring again.
"It's the first time I've fought at Wembley and I'm really looking forward to it.
"I'm getting a lot stronger. I'm still only 20, I'm still learning but in a few years I'll be 40 per cent stronger than I am now."
Khan added: "Medjadji is the French champion and a strong opponent and will come to Wembley to win.
"Every fighter who comes against me wants to win and make a name for themselves now so it should be a good fight."