Khan had been calling out Mayweather before his December defeat to Lamont Peterson and Schaefer said the Briton needs to shore up his defence if he is to win the re-match on May 19.

Khan seems bent on proving his chin after he was knocked cold by Breidis Prescott earlier in his career, going to war with Marcos Maidana and then getting draw into a battle with Peterson.

But Schaefer believes the 25-year-old should play to his strengths and rely on his skills.

"I don't know how to say it more elegantly, but sometimes Amir's balls are too big for his own good," he said.

"Look at Mayweather - he's a master tactician who knows how to use defensive and offensive skills and has been knocking people out recently.

"He knows what it takes to win and fights very smart.

"Amir has the skills, speed and power, but what he needs to work on are the 'ring smarts' and not get carried away.

"He's still very young and he learnt a lot from the Peterson fight. We'll see if he applies that on May 19."