Nothing you can do, but to wait for the next transfer window. A neat trick to help you to get more transfer money, is to go to the Boardroom section, and convert all your transfer money into your wage buget by adjusting your budgets. Make sure you have nothing as a trasnfer budget. Try and lower your total wages spend even more, by loaning players out etc. If you make money selling players, convert that funds into your wage budget as well. Make sure that your balance sheet looks healthy as well, but the biggest thing is to stay within your wage budget.
When the next transfer window open, your board will see that you have no funds for transfers, and when you approach them to make transfer funds available, they should agree with you, and make money available.
On rare occassions, they following might happen:
1. The Board make transfer money available without you having to ask.
2. Then you add all of that money to your wage budget
3. A couple of days later you approach the board and ask them to make funds available. Sometimes they agree.
4. Now you have even more money available
5. Then you go back to the budget section, and convert most of the wage bugdet, into your transfer budget!
6. Happy spending