In hattrick you can have a max dept of 500k €. If after an economical update your balance is -500k of worse you will only be able to login 5 times the next week on to put things straight. After you have logged in 5 times, your team will be blocked. If your financial situation is good enough at the next economical update, the block on your team will be gone. If after that week you're economical situation hasn't improved you simply lose your team.
always keep in mind that using any chpp app also counts for a login.
You are also only able to bid on players or select a new coach untill -200K.