Best way I can think to explain the fungibility of an asset is to say: 1. If you lent me a £10 note, you would be happy with that ten pound returned in any denomination (two £5 notes, ten £1 coins or a £10 note - even if not exactly the same one you lent me), because fiat currency is fungible. 2. However, if you lent me your red 1992 Ford Escort Cosworth RS Turbo (white with go faster stripes btw), you would want that particular car back... not a different one, no matter how similar. That is because cars aren't fungible. Therefor, I'd argue that footballers are not fungible assets, because if Derby were to send us back Will Hughes instead of Andre Wisdom, as much as I'd be happy, a little piece of me would want big Andre back too, the non-fungible gent.