Harrison, who was in charge of the famous class of 92, believes Jones and Smalling will have to wait for their chance to do that.
"It's too soon for them," he told the Manchester Evening News. "I don't mean that as a criticism because I love them both. It's just that there is still quite a bit left in Rio Ferdinand, Nemanja Vidic and Jonny Evans.
"People forget about Jonny, but he's been magnificent the past two seasons.
"At a club like United you've got to be on top form all the time to play on a regular basis.
"Jones and Smalling might have done that but they've had so many injuries that it's been stop-start for them.
"It's about development. They are both young and in another 12 months they should have settled into a position.
"If you are a young player coming through you look at the ages of Ferdinand and Vidic, you're going to think they are not going to go on forever. They've got to be patient."