Smith said in the YEP: "We've got some big games coming up, starting with Portsmouth. We've got to win that one without a doubt. We've had other games this season where people have said that, but we're capable of beating Portsmouth. We have four games left and we'll need to win at least three. I think we're capable of doing that."
Speaking about the United support, Smith added: "They're always going to be there, they always have been. Right from the second division to the Champions League, this club has had great support.
"You can't appreciate them enough. They'll be as disappointed as we are by what's gone on this season. If we played like they support us, we'd by flying.
"There's four more games and they'll be there in numbers, they can sing us to survival. We've conceded 70 goals and that doesn't bode well. But as soon as we finished last week at Arsenal we got it out of our system.
"The point against Everton a couple of weeks ago was vital because that made the gap two points and our goal difference isn't the best. We've picked ourselves up and we're ready to go again. I still believe we'll stay up."