Smith is almost certain to be sold in the summer but had previously hinted he would be looking for a club abroad. "At this stage you can't rule out anything," Smith told BBC Five Live.
"People say that Leeds and Manchester United are big rivals but we're not even going to be in the same division so it's not even a rivalry. I'm not saying I want to walk out of here and go to Manchester United, but they're a massive club.
"If you said the same thing to me about Valencia or Juventus, I'd tell you the same answer. At this stage of my career, if I want to win trophies and I want to do well, then I've got to move on. If I were 32 I'd stay here, it's as simple as that. But I'm not, I'm 23, I've got a lot of football in me and I'm an ambitious person."
Sir Alex Ferguson is thought to be a big admirer of Smith's qualities and would be keen to recruit him as part of his rebuilding at Old Trafford after a disappointing season.