How can I buy a player when I am in red numbers?

How can I buy a player when I am in red numbers?

If you start bidding on multiple players and win most of them your balance could go negative or... You were into a bidding war that ended with much higer price than starting.
To make a bid you only need to cover the starting price.
However you've got 7days to cover the missing money-sell some player/get rewards from competitions and so on.