The veteran spent 20 years at St James's Park as a player, only leaving this summer to join Premier League newcomers Hull City Tigers, and feels that the club's loyal fans have had "their loyalty tested far too often".
Ahead of his testimonial on Wednesday Harper told The Daily Telegraph: "The fans make the club tick but they feel detached from it. Whenever the club has done well over, the fans have been on board. They have been fully behind their team, their club.
"I think their loyalty has been tested far too often in recent years. It's one of the great clubs but it should be competing amongst the very best in Europe.
|20/1||Newcastle are 20/1 with Coral to beat Aston Villa 2-0
"If I had a message to Mike Ashley it would be to engage with the fans, to repair that relationship. It's not totally broken but it doesn't just need a plaster on it, it needs to be fixed."
Harper is fully aware of the expectation placed on the Newcastle players by an expectant home crowd and feels that things could be even tougher this season.
"If things go well, [playing for Newcastle] is the one of most amazing experiences you can have as a footballer playing in England," he enthused. "When there is a good feeling, when the momentum builds, you swim with the tide and you feel unstoppable.
"But when things turn sour, when the club is divided, you're in a rip tide and it's incredibly hard.
"The fans are demanding, even under [Kevin] Keegan and Sir Bobby Robson, they'd get restless if you weren't winning at half-time but all they really demand is you put a shift in. They are working-class people who want to see players put in the same shift they do in the week to put money in their pockets."