The auction system allows you to finish bidding on an auction and buy the player even though you do not have enough money on your account, but you can not place the bid in initial round if you don’t have enough money for that. But You will be credited for the amount you were missing. Your club can be in debt (for example: you bought a player who costs more than the amount on your account) for 7 days.
In case you fail to clear your debt in 7 days, after the 7th day, your players will be sold automatically in order to pay of the debt. The first ones to go, are the most expensive players in your squad (and usually, the best ones). One player is sold each day until your debt is cleared. You can get out of debt by increasing ticket prices, selling players yourself or taking a bank loan. Negative balance: You have 7 days to get out of debt, one good player is going to be sold every day afterward, …