They still need to comply with FFP though, so they need to bring in money to spend money. The easiest way to do it is to sell a player you barely use while his stock is still high.
I read an interesting thing about City the other day. They have the oldest squad in Premier League, apparently. Even when you ignore their oldest players, like Demichelis and Lampard and the likes, most of their star players are either approaching or way past 30. If they keep this up they might collapse just like United did at the end of the Ferguson era.
