Harrop, 21, left United after his Old Trafford contract ran out.
And Pearson, also an ex-United player, told Sky Sports: “With the money being spent at that club it was always going to be tough for him to carry that on.
“He has made a similar decision to me, to come here and play games.
“For many young players that has to be the route if you're not getting regular football at a Premier League club.
“There are two ways of doing it really. You either come down from the Premier League or you work your way up the way that [Preston's former non-league striker] Jordan Hugill has done."