The Championship leaders say Smith, 26, is the man to lead them into the Premiership, according to the Sun.
Peter Ridsdale, who was Smith's chairman at Leeds, is trying to persuade Old Trafford boss Alex Ferguson to let the England star go.
Cardiff fans will not remember Smith with a lot of affection. He was sent off there for elbowing Andy Legg in an FA Cup third-round tie which Leeds lost 2-1 in January 2002.