Football accounting question

I have a question about amortisation of player contracts which I’m hoping one of the accountants on here can answer. Does amortisation only happen on the initial purchase of a player? So, if a player is purchased for £10m on a 4 year contract then there will be an amortisation of £2.5m in the next 4 years of accounts? What happens if the player signs a new 4 year contract some time in that period, is that reflected anywhere other than in the wages costs? Thanks.