Most of a footballers salary is made up of bonuses.When they say a player is earning £200k a week his basic salary may be half that.That is the max he can earn with all bonuses.
Remember Stan Collymore talking about it on Talk Sport once.
Its like with transfers,big transfers are paid off over 5 to 10 years,sometimes years after the player has left.Its how they can get round FFP rules as they are only paying off a percentage each year.Plus few clubs have that actual cash flow anyway as many are running at a loss,us being a prime example.