"We had him as a kid at Manchester," the former Aberdeen boss said.
"He's a talented young footballer.
"We thought we were certain to sign him. But his heart ruled his head, and he signed for Celtic.
"It's difficult to say (if he would have broken through at United).
"But he came down two or three times when he was 14 or 15, and we had his mother and father down to discuss joining United.