There are several reasons Manchester United need to sell some players before the season starts.
The first is to combat wage inflation. There are rules in place in the Premier League regarding the maximum amount a club's total wage bill can rise each season once the wage bill reaches a certain point. United have freed up some room in the budget with the departures of Nemanja Vidic and Rio Ferdinand and the retirement of Ryan Giggs.
However, United's wage bill has been inflating for some time and in April of this year it passed Chelsea's for the first time in a decade, per the Independent. Selling players will allow United financial flexibility when considering new signings.
The second reason is one of quality. Keeping players who have consistently underperformed—or do not appear to have the basic level required to be a success at United—at the club is detrimental to the overall quality of the squad.
The third reason is for the player's own good, allowing them to build a career elsewhere if they will not be used to their full potential at United.
With all these players there exists the obvious caveats that if Louis van Gaal believes he can reinvigorate their United careers, I would certainly not choose to argue.
However, with that said, here are five players United should sell before the start of next season...