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Too early to say if CP will make it with us. We've invested a lot in him so we've clearly got high hopes, but the last player we spent a similar amount of money on (Morata) was a huge disappointment and is now on loan in Spain. Yes, CP is young, but with our manager that's no barrier to selection. He'll have to perform to his potential to earn and keep his place. We won't play him just because we spent a lot on him.
As for the system of buying players, it's just like trading for players in baseball, but 99% of the time money changes hands rather than players. As in US sports, the players are assets of the club they are contracted to, so they can be bought and sold.
Players are not free agents until their contract expires, so clubs do their best to tie players down to a contract to ensure they get money for them if they leave.
The loan system is mainly to develop players, to ensure they get playing time while they are not ready to make it to the first team. Chelsea have probably the biggest squad of registered players in the world, with a huge number out on loan. The club knows that most of these are unlikely to make the first team, but has made a load of money in recent years by loaning them out and then selling them. A good example is Nathan Aké of Bournemouth, who only played a few games for Chelsea but did well on loan, and was sold for £20m. I think the club inserted a 'buy back clause', meaning we kept an option to buy him back in the future. Current players Abraham, Mount and Tomori have both played a lot of games on loan at other clubs, and the club is now reaping the benefit of that experience.