If you purchase a player and spread the payments over x amount of months, do you need to have that full amount available when you make the offer for the deal to go through?
If you offered £40m over 48 months all you would need is £10m to cover the first twelve months payment. But then the following three seasons, your transfer budget is reduced accordingly to cover this.
Just a bit of advice, you can always snap up Arturo Vidal for around 2mil because Leverkusen don't need him and put him up for transfer, that's if you're in the first seaosn.