Someone buying a player with not enough money or space in team.

[Potemy]

You can bid for any player as long as you have money for the initial bid. He might have signed another player or started construction since he put in the initial bid. If you get the player, you will have a negative balance, and after 7 days, the bank will start to sell your most valuable players, one a day, to get you back to a positive balance.

The signed player will be in his squad page, but without a contract, like having a youth. You have 7 days to tie him to a contract, otherwise he goes as a free agent.