The former striker turned pundit spoke about United’s treatment of manager Erik ten Hag.
The Red Devils spent weeks assessing Ten Hag’s position at the end of the season, before choosing to retain him.
“It's been confirmed that Ten Hag will stay on as the manager of United,” said Shearer while speaking to Betfair.
“Considering he had a bit of a pop at pundits after the FA Cup final, it was really interesting to see him being a pundit himself on television recently.
“But what a mess it's been. How kind of United to go to Ibiza and inform him that he's still wanted as the manager, and then tell him that they've even spoken to other candidates.
“It's just a bizarre situation, it's not how things should be done in football. If you're going to speak to other managers, then speak to them, but keep it in house - you can't let the public know.
“To be undermined like he has done, I know they're now saying that he has their support and they want him to carry on, but from a personal and human point of view, it's not the right way to treat someone.
“It takes a lot of his power away from him. Will the players look at him and think he's a really strong manager and he's in a strong position? Probably not, because of the way they have treated him. It was meant to be all new at Old Trafford with the very best coming in - I don't think they've got off to a good start.”